^Yep overwhelming consensus on the helicals is bad. The races are too shallow on these little bearings for anything more than moderate side loading. Like Neil said they'd have to incorporate a thrust bearing, which would require preload to work in the radial axis. Scaled up just a little the helicals would be superior to straight cut, but size is the limitation. In that vain I don't think I'd wanna drive a 1:1 with straight cut gears...
Some info on compatibility here-
http://www.rc-monster.com/forum/showthread.php?t=23255