I was using their electronic book for number theory and inequalities and I loved it. It costs $7 or something like that. Of course, it was ust a suplement to OG and
MGMAT but I've found it very useful.
Unfortunately, I don't have experience with other 4gmat material, but uf it is anything like the book i described it should be awesome. I just hadn't enough time to order those books because I've learnt about that company pretty late. Nevertheless, I'm sure that little electronic book added 2-3 points to my math scaled score. It contains some very advanced concepts I wasn't able to find anywhere else, and some of those concepts are actually tested on 46+ level.