Regarding the SERPA, when I had one, I lined the inside with two strips of felt to protect the finish. The Safariland ALS has a full inner lining of suede (stock).
I did buy the Safariland ALS after I had my SERPA for a while.
Regarding the two, I'd recommend someone buy the ALS over the SERPA. The draw is just as natural and fast (more so, if you ask me). You can add an additional "level" of retention to the holster by adding on the "ALS Guard". The ALS holster is more "stable" (less jiggling of the gun in the holster) that the SERPA (My gun is a Springfield XDm 9, YMMV)
The only thing I don't like about the ALS is the holster itself is bigger (more mass) and this has some drawbacks for my situation (like the bottom of the holster can dig into the rise of my bucket leather sports car seats if I am not careful). However, I think this increased mass helps provide my stability.
Again, YMMV. I don't care if you like the SERPA better, I don't. These opinions are my own. You're entitled to yours.