I looked it to this quite a bit before doing this conversion, The case difference between the super and the 9mm is minimal and the approx. .004 difference between the 9x23 and the 9mm adds up to .002" less material between the chamber and the O.D. of the cylinder. Not enough to make it too weak.
About the safety issue, by compairing the pressure between the 9x23 in a closed chamber auto and a revolver. you'll find that since the bullet doesn't need to be pushed over 4 inches down a barrel (in a 1911 pistol) the same amount of preasure does not build up.
In a revolver, the bullet travels approx. 3/8 of on inch and then crosses the cylinder gap. This bleeds off quite abit of gas which greatly reduces the built up pressure in the case. Add this to the fact that you are pushing the bullet down a barrel that is only 2.5 inches long and this reduces the pressure (compared to that closed chambered 1911) even more. (check out the velocity difference between a 1911 and a 4" revo chambered for 9x23).
All this said, I always insist the user carrys factory ammo, and if they reload, to load lighter than factory loads for training with the gun.
The .38 super or 9x23 does give you quite the little power house pocket gun with the ability to use moonclips.
The conversion is $89.00 (need cylider only) plus $3.95 priority mail return shipping.