I have installed 4 Mcarbo kits in all my 75's years ago without any additional polishing, and IMO, each of those 75s now have a trigger that is comparable to the Shadow 2. Thousands of rounds fired with no problems. For every naysayer, there are 50 that are extremely satisfied, just read the reviews.
CZ 75 Trigger Spring Kit review-stars (4.78 out of 5) 488 reviews
All I'm saying is that in my experience, MCarbo doesn't appear to have the consistency and QC (especially for springs) of other suppliers... Don't know anything about spring manufacture, so no idea why.
And I have more confidence in their hard parts (but even here have some minor gripes about their close copies of pre-existing offerings from folks like Tandemkross, Galloway, Tacticool, etc.).
Further -- I also believe that marketing/what sells seems to drive their product offerings, not reliability or a specific product focus. Their price-points have their springs business as a volume sales game, and their gimmicky marketing seems to reflect this.
Don't get me wrong -- I have been and will continue to be a customer of MCarbo, but I think it's a bit of a buyer be aware/go in both eyes open situation, not necessarily a Buyer BEWARE situation though...
Especially since I have seen, on several occasions now, MCarbo doing some censoring/suppression/removal of various customer gripes in both their Brotherhood Forum and their Facebook Group.
Personally, if just a range gun or no other options available, then go w/ MCarbo springs. And feel free to buy whatever else you want there too -- but me for instance, I tend to make MCarbo my last stop for upgrades for those parts not sold elsewhere OR those that are uniquely better or different.
As always, YMMV.