I still have 2 quads, one in 22lr and 1 in 17hmr, both in T4 stocks with KMW cheek hardware added by Joe Ducos (stock doc), KRG 2 stage triggers, lilja barrels, as well as dip bottom metal, A419 rails, and sterk AI style bolt handles. The 22lr is used for targets and the 17hmr is primarily for small critters out to 175y or so.
Both shoot great and are nice actions to run, but I do occasionally think of building new rimfires on R700 style actions to have more options for stocks and triggers.
Not convinced it's worth all the money to do so though, as I don't shoot .22 NRL matches where a different stock and a long heavy profile barrel would be nice, and it's the quality of ammo, not the rifle, that is the limitation on the 17hmr. Both quads do the job just fine for me.
This thread reminds me that I should purchase a few more spare parts for the quads; maybe a spare magazine well assembly, firing pins and springs, extractors, etc, as getting parts can be difficult (thanks Beretta USA for your awesome customer service, lol)
I keep eyeballing the RimX as well as the 457, but haven't decided to spend the money... Yet.