Either way, you should get the arrow spinning.
I have a Jo-Jan with a straight, and a RW helical clamp. The helical is not bad on 11/32 and larger shafts, but it was a pain to set up on 5/16, for my daughter's arrows. So I set it back up with the straight clamp with an offset. That way I can just adjust it for either RW or LW feathers. Much less hassle and the arras fly great!