Some "clarification" re the 2 mag bases I now have. They are both now attached to the CA-legal, 10-round, factory mags that came with the pistol. The pistol is for home defense, not run and gun where I might be dumping mags into sand, dirt, mud, etc. I have zero expectation of getting the mag interiors dirty and no plans of every cleaning those interiors. And I have no expectation of slamming home a mag with sufficient force to overcome the position of the spring and sliding off the base. I seriously doubt that doing it unintentionally, i.e., without a tool, is even possible.
BTW, installing the base is not a snap, the blood I drew trying to restrain the spring while engaging the base attests to that. I turned up, post-bandaging, using one of the handles of a pair of insullation-wrapped pliers to hold the spring down while sliding on the base.
In regards whether the magwell is the right one for my CA-legal, SP-01 pistol is still to be 100% confirmed, though I am very sure it is based on the Armory's product page text. The pistol is due back from CGW on Friday at which time I will try to install it. In talking with Armory just now on the phone, they confirmed it is a CZ factory part they sold me, not a part they manufactured or sourced elsewhere. It sure looks exactly like what is shown on the CZ (factory) product page. That said, the text on the CZ product page is very uninformative, "ALUMINUM MAGWELL LARGE FRAME BLACK". [I bought from Armory because CZ had no stock.] Seems, from what you say, "large frame" for CZ means "wide frame" not "full size", as is full size 75. Seems I got lucky in going to Armory.
Interesting side note/question - since the 75 SP-01 is available in both low-cap configuration (01152 - what I have) with 10-rd mags and "regular" configuration (89352) with 19-rd mags, doesn't the "regular" version need a "wide frame" to support the 19 rd mags? Thanks.