The gen 1 and 2 Brodak ARFs suffered from approval of prototypes that was too hasty, I believe. There are several instances where inches to metric translation suffered.
I know that John has recruited a team that has worked tirelessly on improving the earlier pieces and on trying to bring the very best in the next generation....
A 1 3/4" is what most are using. The Brodak aluminum spinners are nifty, except that they are cut for 6 pitch props and need work to run with modern engines...
Have fun!