I had my Jimmy crystal and the standard rep crystal tested by my watch-smith on hardness. The Jimmy crystal was tested to have a hardness of around 4 and the rep crystal was tested to have a hardness of 9.
The conclusion of my watch-smith was that Jimmy's crystal was mineral glass and the rep crystal was genuine sapphire crystal.
Jimmy's crystal:
~ Much taller then rep crystal or davidesn crystal.
~ Teflon ring thicker the rep crystal or Davidsens Teflon ring (Jimmy Teflon ring wont fit the rep bezel)
~ No AR what so ever, looks like clear glass.
My conclusion, Jimmy's case's, crown guards, bezels are the best after market parts for Panerai, but his crystal is crap. You need all Jimmy or Jimmy and OEM parts to make things work. Jimmy parts don mix with the standard rep or Davidsen parts.
I have attempted to build a PAM111h with a Jimmy case, bezel, CG, palp crown and Davidsen crystal.. The results are O.K., but the Davidsen crystal is to short (the crystal sits flush with the bezel instead of sicking out ~ 0.5mm, see pic)