Just a nitpick FWIW, there are two different conversion kits available to fit the 938, One with a 3.3" barrel, and one with a 4.1" barrel. Unfortunately, the Sig website fails to mention this fact.
I think it's reasonable to assume the more costly kit is the one with the 4.1" barrel. Also the shorter barreled kit used to have night sites instead of adjustable target sights. I don't know if this is still the case. Sigs website is woefully short on specifics.
Anyway, I have a 938 and a 4.1" adapter kit and like it. It is a little picky about ammo, not liking lower power stuff. I tend to just feed it CCI and save the low velocity stuff for my revolvers.
Edit: According to a video of a Sig guy at shot show, the long slide version has a 4.4" barrel.
I'm too lazy to go dig mine out and measure it.