Opinions vary, but the helical may provide some edge – mental or actual, at distance with broadheads over a 1.5 degree offset. I have had good success with both but I go with the helical just in case.
You lose some speed at distance with helical due to drag – for my setup and within my shooting ability, shooting helical against 1.5 degree offset at 40 and 50 yards, all else being equal, I see no percievable impact difference.
I fletch everything RH heilical and set the off set as far as possible so as to get good contact with the shaft. The off-set changes with different size shafts, so it can not be a standard.
I put the vane or feather in the clamp on my Bitz, and without any glue, I adjust front and back and hold up to the light so as to check for good contact at the base. I bought my Bitze jig’s over 40 years ago and back then they cost just under $20 each and got both styel clamps with them. I see the cost a bit more today, but the old guys still work good.