They are just about as reliable as the other mvs boards IMHO. Having more slots means more chance of a slot problem sure, but overall they are not that troublesome.As candycab mentions keeping the slots and cart contacts clean is important.
Also if you do not have all the slots occupied its a good idea to cover the empty slots to prevent dust and stuff getting into the boards slot sockets, you can use masking tape for that.
The only problem Ive had is the 5volt track on the jamma connector gets hot and toasts eventually carbonising leading to intermittent operation, its an easy fix.
All in all I think you will have no regrets with your purchase. More slots-more fun
