I've tried more than a dozen different diapers, but pretty much used BumGenius exclusively. I started with 2.0s, replaced those with the 3.0s and almost replaced those with 4.0s. But, this time around I wanted to go with something organic, and I have to say, I'm really liking the Flips. I bought 12 covers and 18 organic liners. I could probably have done with 8 covers and 20+ liners instead. I don't think I'll have any need for the disposable inserts, but they do have them. They fit just like the BumGenius, but they are just a cover with a folded prefold in them. The only thing that I don't like (but is unavoidable) is that when DS has a major BM poo, it doesn't absorb at all, and because it's just a folded insert, not a prefold folded around him, the liquid poo kind of gets everywhere. He hasn't leaked at all, but the poo pools along the leg gussets.
As for the 4.0s, they are definitely better than the 2.0s. The best part about them is at the top (by the belly button) they have a line of PUL, so you don't get any wicking when baby's wearing something with a waist band - something that often happens with my other diapers. They are bigger too, so they will last longer. And, there are such cute prints, compared to the 6 that they used to offer. If you like the 2.0s, you will definitely like the 4.0s.