Apologies in advance for being long winded...
There are really two levels to any discussion of diet for their fish. The first is what they normally eat in the wild and is basically comprised of natural foods that is not processed or fortified in any way. The other is what they are fed in captivity. This gets more complex for lay people. It is one thing to say a fish eats inverts and a completely different thing to analyze what nutrients etc. that invert supplies. The folks who know this sort of information wear white coats and works in labs.
And then we come to the fish keeper and having the need to feed their fish a healthy diet which supplies the things they need. How do we wade through all the manufactured foods out there? And what complicates this all is the disconnect between the science side and the manufacturing side all if which is complicated by the urban fish myths about it all.
The problem this dichotomy creates can make it difficult to work out a proper diet for out charges. Some argue that ingredients which a fish does not eat naturally should be avoided. So something like garlic would certainly fit that bill. I would bet there is no fish in the wild that has garlic in their diet. On the other hand I can find plenty of research papers dealing with garlic and fish- both fed or in the water which conclude that garlic is beneficial.
Finally there is a difference between how the average keeper feeds their fish as opposed to how the sort of folks that are members here who are working to have fish spawn feed theirs. Folks working to spawn their fish need to insure they are fed a proper diet designed to make fish physiologically ready and inclined to spawn.
At some point after a number of years of keeping fish and reading things all over the net, one day I asked myself, how do I know this stuff is true? This led me to a wonderful thing called Google Scholar. It is a repository of research and knowledge. I also began using more sophisticated sites such as planetcatfish, finarama, erc. There are a number of top grade scientists and fish experts on such sites.
I learned that I needed to feed young Hypans more veggies than I do with the older ones. I also read a few books which helped me better understand how various plecos feed in the wild and how they have different dietary needs and adaptations. I learned that things were not always as simple as they appeared. When the algae eating fish rasp algae, that algae is full of tiny critters that would qualify as "meat." I watched my meat loving clown loaches take chunks out of anubias. I learned that a diet primarily consisting of veggies does contain protein.
The reason I use Dr. Tanner's Fruut-Luups is simple. I know he has the education and experience to be well informed on this topic. I also know that fish eat a lot of things that we may not realize. In the wild many things fall into the water from fruits and nuts to insects and animals etc. It makes sense that some fish take advantage of this. I know that fish eat crustaceans and insects and larva. Plus I have had the pleasure of attending presentations he has made on fish diet at weekend hobby events. The reason I use Repashy is that several people I respect use it, including some very successful breeders. Btw- look at the ingredients in Fruut-Luups and you will see:
FRUUT-LUUPS is composed of Papaya, Mango, Organic Banana, and Fig. The fruit is complemented with easily digestible Black Soldier Fly, Krill, and Squid that attract even the finickiest feeders. These top-shelf ingredients make up >75% of the food. Fortified with our new Nutraceutical Premix made from Mango, Dandelion, Stinging Nettle, Garlic, Ginger, and Cinnamon based on published peer-reviewed research.
Most of us are hobbyists and we do not make a living from anything related to the hobby. This often means our time is limited in terms of how much we can devote to the fish. So we often fall back on the easiest solution. It is a lot easier to feed flake food than to batch up Repashy, insure it does not spoil and then feeding it is a bit more work too. It becomes very easy for one to get lazy and begin feeding what is easiest rather than what is best. This doesn't mean we are mistreating our fish, just that we may not be giving them what they need to spawn.
In the end, one must figure out what works for them. Even though I know live foods are best, I do not feed them. I have done red worms and I have hatched out bbs. I stopped because it was just more work and I had to draw the line somewhere. Initially, I did a lot of frozen and had decent success. Then I got lazy and I got way fewer spawns. My fish didn't die or stop growing, they just slowed or stopped reproducing. Now I am using Repashy.
I suppose I could go on about the various ingredients in the Repashy mixes. But in the end what matters is feeding it has provided what my fish needed to get jiggy again. One of the attractions of the food is it is ideal for my Hypans of any size/age. As long as a food is soft and can have anything from a tiny fry sized bite to an adult sized chunk easily eaten, it is ideal for use in spawning tanks in which the fry are allowed to grow out with the adults.
There is one downside to feeding Repashy, it is not cheap. But I am not feeding it exclusively. My fish still get a variety of foods which includes frozen and more commercial things like flakes, sinking sticks or bits. I do make my own flake blend using a mix of several foods from kensfish. I mix his basic flake (about 50%) with veggie flake (20%), earthworm flake (20%) and immune booster flake (10%). The best way to show this cost- I spend about $125 a year on frozen foods. I just spent that to get about 4 pounds of Repashy mixes. I do not expect this will last me much more than six months. (I have 12 tanks devoted to Hypans. and 8 to other things.)
Tip- Fish are not very bright, but they are not complete idiots. Often what gets a group of fish eating a new food is seeing another fish eating it.
As for the differences between the Repashy Grub and Bottom Scratcher- they have similar and dissimilar ingredients. The Grub has less protein end more fat than the Scratcher. Both contain insect meal as a main ingredient. The neat thing is you can shoot Allen Repashy an email and ask questions. He answered mine immediately which is why I purchased the Bottom Scratcher.
This is what I do because it works for me. That does not mean I have found the single best way. There are plenty of folks out there who do things differently and with greater success. I have always considered myself to have been more lucky than smart when it comes to all of this.
Edit: it occurred to me that I omitted a simple method for comparing fish foods. Read ingredient lists and compare them.
As long as it is not freezing outside, I tend to let it cool there. 
