I never got the hang of swiping with both thumbs: it seems like there's a timeout where if you take too long between letters it decides you're done? Or something? And when typing a long word, the whole keyboard gets so covered with glowy Tron psychedelia that you can't even read the keycaps any more. There are popup menus for correction where you're expected to pull down then move left or right, and inevitably the thing you're trying to find is occluded directly under your hand, no matter which hand you use.
I remember finding on-screen keyboards initially incredibly frustrating, but I don't think it was this frustrating. At this point I think what I really want is just one that has much better text prediction. (the stock iOS 8 keyboard is enormously better than iOS 7 in this regard.)