I run wombolts, and havn't had any problems, other than the bolt that you do them up with loosens over time, it doesn't loosen dramatically, but every now and then i tighten it about a quarter of a turn.
They are extremely easy to install, took me under 10 mins including pressing my bb and spacing it all correctly....
If i ever buy cranks again it will be these, or the fly cranks, 2 piece is awsome!!!
and yeah their $350, the fly cranks are the same also... but i prefer the wombolts