I've had this one (it's not my first) for a little over a year now...wonderfully accurate and a cheap way to get some DA/SA trigger time that directly applies to my M19 & M66's.
In my hands and off a rest it's as accurate as my M41 Smith, yet doesn't take match grade ammunition to make sub-2" groups at 25 yds. It truly is a great gun. Over the past year, I've been using it to coach family and friends on DA/SA revolver shooting...in that venue it's superb.
I've also had a Colt Diamondback .22 lr with a 4" bbl. for over 25 years. It just doesn't compare to the M18 Smith however. DA stacking in the trigger release is my prime complaint with it, that and it just isn't as accurate with any ammunition.
The only drawback to a Smith M18 that I've found is that the cylinder chambers are extremely tight...tight enough that ejection can be difficult with certain brands of ammunition. I keep the chambers clean and have polished them as well, and this makes it not much of gripe anymore.
If you're looking for a top-drawer .22 revolver, I don't think there's any that can compete. Too, it's 4" bbl. makes a great small caliber trail/plinking gun. M18's aren't cheap by any means, but I'll bet you'll never part with one if you take the plunge.
First pic: M18, 2nd shows it in comparison with my Colt Diamondback .22
Best Regards, Rod