I have a Ciever, two Marvels, a Jarvis and a Tactical Solutions conversion kit. I also did have an original Colt unit.
The original Colt unit is all steel, plinker in terms of accuracy and has a floating chamber which is a pain in the neck to clean.
My Ciener unit came with a smoothbore barrel which they replaced. It has functioned well with several ammo brands. Accuracy wise it is slightly better than the original Colt unit. Customer service is nonexistent as I found out with my Ciener Glock17 unit. The Ciener magazines are well made.
The Marvel unit#1 is a favorite of the bullseye shooters, superbly accurate, extremely reliable with SV ammo, slide is aluminum and does not lock back after firing the last round. This is my favorite unit. I have one set up with iron sights and the other with a red dot. You can purchase an extra heavy recoil spring and use the Federal copper washed bulk pack HV HP ammo.
The Jarvis unit is all steel, prefers CCI MiniMag or Remington Golden Bullet, slide does lock back after last round, it has been discontinued. Accuracy better than Ciener or Colt but nowhere near that of Marvel #1.
The Tactical Solutions unit is an improvement on the original Jarvis, superbly machined from steel, somewhat picky in terms of ammo preference, CCI MiniMags work very well, some problems with getting the slide to lock back after the last round. The barrel rib extention does case an occassional ejection failre. Accuracy is on a par with the afformentioned Jarvis unit.
I have an Advantage Arms unit for the Glock-17. It will function reliably with CCI MiniMags or Remington Golden - you have to put up with the usual ignition failures using Remington Golden.
Hope the above helps you choose an appropriate unit.