Mostly, guys who were able to get CDI to do bottom metal for their rifles years ago are holding onto them with their lives. Some of us got the TBM kit from FN. It was almost always wildly overpriced, but for some reason a few months ago MidwayUSA got ahold of some and sold them at $240 (usually twice that if available). I certainly jumped on and got another one.
For years I used the old factory DBM and it worked quite well. I definitely didn't like the OAL and capacity limitations though...but they were generally very reliable.
My SPRs (3) have all been pretty good shooters. The only one that was an absolute hammer is still in factory form. The other two have since been rebarreled. I'm a huge fan of the SPR for the money they sold for a decade ago...even what they go for now.