I don't have one for the 19/23 frame, but I did have one for the 17/22 frame years ago. There were things about it that I liked (accuracy, reliability and "cool factor") and things I didn't (cosmetics, weight, lack of accessory options). The most serious issue was the vibration I'd get in the stock (and therefore in my cheek) every time the gun fired. After a couple hundred rounds, the entire side of my face would be sore. The plastic stock insert and nylon cover help mitigate this, and should be considered required accessories.
Looking at the Mech Tech website, I see that not a whole lot has changed since I had mine... the stock is now detachable (mine was welded on) and a few additional styles are available, but I think the standard fixed stock with the insert and cover would still be the way to go. Offering a lighter barrel, threaded muzzle option, and integral low-profile iron sights would, IMO, make this conversion kit a LOT more appealing.
In the end, my 9mm AR took over for my pistol caliber carbine needs. It was lighter, more comfortable to shoot, and didn't require disassembling my Glock or keeping track of a little feed ramp block in order to use it. I sold off the CCU and don't miss it a bit.