Whitey, you left out the, um, best part. AAR 620s will give nine (9) shots on a 120 roll. If you don't believe me, run a scrap roll through and mark the edges of every frame.
bowzart, AAR 620s slip in like cut film holders, are the best solution to shooting roll film on 2x3 and 3x4 cameras that have spring backs. The very similar Calumet C-2 is for 4x5 only, bot most of the ones sold shoot 6x7. 6x9ers exist, are uncommon.