... and used the Mecgar 15 round P229 magazine to bump its capacity. You can covert a existing P228 or P229 into this gun at a much lower cost IMHO.
Actually this is technically not true.
The M11-A1 is based on the .40/.357 P229 frame that uses a wider mag. The A1 gets its 15 rd capacity by using a wider P229-1 mag instead of the lower profile follower and spring in the previous 15rd Mec-Gar mag for the P228/P229, even though I believe Mec-Gar also makes the M11-A1 mag. Also, there is the problem of locating a stainless steel slide with full height serrations that will fit the P228 and older 9mm P229 frame.
However, I am not saying the M11-A1 is better, just slightly different and not easily replicable using an older P228/P229 frame, assuming someone really wanted to do it. The M11-A1 is probably as close as you can get these days if you want a new
P228, short of finding someone's safe queen on GunBroker.