I have not purchased a conversion kit, however I did succumb to the temptation to buy a .22 LR version of a SIG pistol, a Mosquito. Unfortunately I found it to be unreliable with anything less than premium ammunition (e.g., CCI Mini-Mag), and with mediocre accuracy at best. The feeding issues diminished with use, but the accuracy never improved.
For me, .22 LR is capable of superb accuracy at relatively low cost. Since it has low recoil, it is an excellent tool for introducing beginners to the art of shooting, including stance, sight alignment and trigger control. What it doesn't do is provide any useful training in the manual of arms for a center fire pistol, despite any superficial resemblance.
In order to achieve an high degree of accuracy, a dedicated .22 pistol will have a barrel rigidly attached to the frame, as well as the rear sights. It will also have a finely tuned trigger.
Despite the fixed barrel, my Mosquito has poor accuracy, which I attribute to the slide-mounted sights and rough, heavy trigger. Many of these attributes are found in conversion kits as well.
You get better results from relatively inexpensive .22 LR plinkers, like the Ruger, Buckmark and others. At the other end of the scale there are precision works of gunsmithing art in the S&W 41, Colt Woodsman and High Standard pistols. With them, you can aspire to the quarter-sized groups at 25 yards of the master marksmen, instead keeping them in the black (or on the paper). After 50 years of lusting and procrastination, I now have a classic K-22 Masterpiece (c1954).
Now if only the quality of ammunition had maintained the same standards.