I dont like the unit 1 just because its not a standard slide... I was shooting one after swapping guns at the range one day, and went to rack the slide after reloading. Got a nice little cut from the rear sight... didnt really hurt, but it annoyed me for a few days being in my palm.
I would prefer a unit 2, Wilson, Kimber, Advantage Arms standard, etc. Still a 1911, so to speak.
I use a Ceiner that I had a local 'smith install a Novak front and hidden Bomar rear sight in.
Advantage Arms will slide lock on empty, never used one though. I thought it was an option on the Marvel... Wilson and Kimber, probably not. The ones I've seen looked to be based on Cieners. You can still lock the slide back, but they won't do it for you.
Note: at one time Ciener (a firm that has irritated a lot of customers, but once built a lot of good units) also built a lot of the units sold under different names for big gunmakers. I suspect that a Ciener sold by another company (with that company's name on it) will get you good after-the-sale support if you have problems.
Ciener made the early kits for Kimber, and I think Wilson as well. Rebranded Ciener conversions didnt last though. Most of these companies either outsourced to someone else or started producing them for themself. One thing I see when looking for magazines is "will not work in 'blue box' conversions" or something along those lines.
CIener: Great products, from a terrible company.