I bought a .22 lr conversion for the SIG P210 here in Switzerland last year
I resisted for a long time since they are quite pricey. This one was $ 950, which is a lot for a slide, barrel, guide rod/spring and one magazine. You can buy a nice gun for this money, even almost a milsurp complete P210.
However I finally gave in, as the .22 lr complete pistol (the SIG P210-7) is over $ 3’000. And since those conversions are not produced anymore it will likely hold its value.
Mine came without the box, which is a blue cardboard similar to the ones the pistols shipped in. This pic is from the internet

So here’s mine


The guide rod has the caliber on it

The barrel and slide are numbered
The barrel doesn’t have locking lugs like the big brother, it’s a simple blowback


The top rear of the slide has a depression / cut in front of the sight to reduce weight

And reliefs under the front sight


Here’s a side by side comparison with a regular slide for 7.65 and 9 mm parabellum



And here it is mounted on my P210-1. The fit and finish is excellent, as I expected from SIG of this period






I took it to the range and I was impressed with both the accuracy at 25 meters and the reliability with CCI Minimag.

However I went a second time with match ammo and the reliability was not as good, seems it did not have enough energy to operate the slide reliably.
But I am very happy with this acquisition. One of the shooting club I frequent dedicates Tuesday to .22 lr, and I am having a lot of fun with this.