I just purchased a Sig 1911-22. It has performed flawlessly so far and digested every brand of ammo I have fed it. It is a full sized 1911 pistol and all the controls work just like a regular 1911. The feel an weight is the same as my .45 1911s. The magazine is built like a battleship.
The Browning is the same but scaled down in size.
The only reason I chose the Sig over the GSG was the Sig offered more of a choice in grips and colors. If that doesnt matter to you go with the GSG and save some $$$ over the Sig.
You will have a blast shooting it and save yourself some $$$ on the ammo. Great trainer for the 1911.
Some of the notable differences, the sig/gsg one uses a zamak slide, but are full sized. The browning is scaled down a bit from a full sized 1911 (85% the size if i recall correctly) but uses an aluminum slide. Zamak is a deal breaker for some people, but they all seem like neat 1911-22's to me
If getting one for myself I would go with the sig/gsg for traditional size specs.
Most of those buying the 1911 style .22s do so because they have real 1911s in centerfire calibers and use the rimfires for practice. If that's the rationale, then the Sig/GSG would seem to make more sense.