As long as you understand that it won't really be effective against anything larger than a rabbit, I think it's a fine choice. As much as I enjoy shooting my 6 inch 617, it is a bit heavy for long distance carry as a sidearm, which is why I'm looking into a chest or shoulder holster for it.
BTW, if your thinking of using shotshells as a defense for rattlesnakes, think again. Shotshells don't pattern well from a rifled barrel and with a 22 caliber shotshell you'll have to be well within the striking range for it to be effective against a rattlesnake. A much better choice would be to make enough noise to cause them to avoid you or become very accurate with standard 22LR.
BTW, if you do find one make sure to post back. My impression is that the 617 is the 22 that is produced in the largest volume and the other 22's are basically afterthoughts, so it might be a bit hard to find. Now, that I've become a bit hooked on shooting 22's, I find the model 63 a very interesting little gun. I'll bet they are a joy for DA practice and suspect that they may prove to be just as accurate as the 617.