Yes, we have been using Duocal for over a year now. I have trouble finding things to mix it with. But, I do use it daily in YoBaby yogurt. I put 3 scoops in a 4 oz container. It does not mix well with Pediasure, applesauce, cottage cheese, juice. But, we always do well with the yogurt.
I have to be honest and say that I haven't noticed any weight gain. If anything, it helps maintain the weight he already has. I had high hopes of him packing on the pounds with it, but that didn't happen. It has 25 calories per scoop (roughly 1/2 tablespoon). My rationale is: it's better than nothing. And, in our case, it is better than butter or oil, because he just poops that out. At least the Duocal doesn't cause diarrhea.
I have thought about adding it to his feeding bag overnight, but thought it would gunk up. So, I haven't tried that yet.
I was able to get his insurance (Medicare) to cover it, but it took some work. Otherwise, I believe the cost is $80 per case. Each case has 4 cans (the size of baby formula cans). Once opened, a can is fresh for 30 days.