I've turned both drilled and slotted with no problems.
The feed rate and cut depth are the key to making them work.
As for triangle tips vs. round ones, I can't speak for the round ones, but the contact point is going to be the same. I can't see these making much difference. Locking up a brake lathe on a cut is an indication to me that the cut depth is waaayy too deep. Slow speed and about .002-.003 and you'll cut them just fine.
