I like 22 conversions in general and have units for the Glock 19/23 (Ciener), CZ-75B (Kadet), 1911 (Marvel) and a DPMS AR 22lr dedicated upper. However, I can not recommend the Ciener unit for the Glock. Mine has never run reliably with any ammo. It works best (when it works at all) with CCI Stingers but they cost more than my 9MM reloads. The other problem is that the 22magazines do not fit in 2 out of 3 Glock frames i've tried it with. They fit in my very early G-19 (1987) but have to be pried out of my 2ed gen G-23 and tools must be used to remove them from a 3rd gen G-23. Overall, not worth the price.
On the other hand, I have heard nothing but good reports from the Advantage Arms units.
Hope this helps.
JAC