I have one of the old Beretta-made conversions, and one of the newer Umarex products. They both shoot about the same (from a rest, they will use all of the black on a NRA 50 ft target), but the Umarex magazine can be easily loaded without the tool the Beretta conversion requires. I believe the Umarex magazines will be more durable than the Berettas because the ejector is on the Beretta .22 conversion magazine, the way it was on the Walther P38 conversion magazine, and that eventually broke on the Walthers.
I do regularly use the larger and easier to load Umarex magazines in the older Beretta conversion, and they work 100%, seemingly the rim of the top cartridge in the magazine acting as an ejector
Neither of these is match quality. I have both a Nelson and a Marvel conversion for the 1911. With ordinary standard velocity CCI, they will hold the 10 ring on the NRA 50 foot target.
My first pistol was a Walther, and I've bought a lot of their products and been really happy with them. I was not pleased to hear that they had been bought by Umarex, but then I bought one of their top-of-the-line .22 target rifles, a KK500. My daughter teases me that it is a Nerf Gun, but it shoots like a Laser.
The only bad thing I can say about the Umarex conversion (and about the older Beretta conversion) is that a lighter hammer spring, which I usually install to improve centerfire double action trigger pull, will eventually impair ignition when the .22 conversion is on top. Ernest Langdon as developed a number of improvements for the Beretta 92, some being sold by Wilson Combat, some by Langdon's LTT. Langdon developed an improved trigger bar for Wilson, then improved it some more in one he offers. During double action, the trigger bars cause the hammer to arc backward further, so they store up more energy for the same weight hammer spring, and Langdon then can get away with a lighter hammer spring storing up the same amount of energy in the hammer. It works great in Centerfire, especially with Federal primers, but at the lowest spring weights it does not work with the rimfire conversions. The stock Beretta 92 hammer spring is 20 pounds, with a DA trigger pull of about 15 pounds, although there is a DA-only "D" version of the 92 which comes with a 16 pound spring. which will ignite all the .22 rimfire I have tried with it. With a full Langdon trigger bar and other improvements, and a hammer spring of 12 pounds, I can get all Center fire primers to ignite and my DA trigger pull is about 7.5 pounds. ...but most .22 rimfires will not ignite.