The rule of thumb is the further back the vanes are the more stable the arrow will be.

Also, the more offset they put on the vanes the more they will spin.

In both cases you may have to tune your set-up due to a slightly different flight. However, the flight difference may be so small that you do not have to do a thing to your set-up.

All of this just makes the arrow more stable and helps with tuning issues.

If tuned properly you shouldn't notice a difference between the 2 arrows. You might be able to see the one with more offset rotate more at longer shots but that's about it.

i shot my buddy's arrows with helical and mine with just offset and when my bow was slightly out of tune his arrow flew better for me. After correcting tuning issue and the only difference was the amount of spine on his arrow. They both flew well even in wind.