I've used them, they form part of our regular stash. I've found the inserts to last a little longer on my LO then the BG at times. Plus the fleece inner feels a lot better and thicker than they do on the BG. I must say I think the BG size wise are a bit bigger, I've found the rise on the rumparooz to be a little smaller and my LO was on the second to last snaps whilst still on the lowest snaps in the BG. I think this is because rumparooz are supposed to be used for little tiny babies though so they go a little smaller.
Saying that I will probably end up getting some more in the future.