Yeah- they are not cheap, but they are definitely built to last. My wife bought me the .22 Hunter almost a decade ago for $375 and they are close to double that now. Despite a decade of use, it still feels like it is brand new.
I have a CZ512 in .22LR and it is a tack driver. I polished my trigger components and drilled a spring hole as in this guide and it made a huge improvement. http://www.rimfirecentral.com/forums/showthread.php?t=397948
Trigger still isn't great like some of my CZ's, but is better than average...
I've had one since spring. It is very accurate and the action is smooth. I had an issue with an overtightened grip panel from the factory, but Ruger replaced it. It is a nice little hunting companion.
I have the standard SP101 kit in my 2012 SP101 .22 and it said the same thing when I bought it. I think that Wolff's concern is that the hammer springs are too light to reliably ignite the .22 ammo, unless you do a polish job when installing it. If you just put in the spring kit you will have...
http://www.teslamap.com/public/sp101_trigger_job/index.html
Use the above guide and the Wolff spring kit, and the 12# hammer spring should work (8# rebound). If you experience light strikes, you can use a stock SP101 spring from the 357 model as it is lighter than the .22 SP101 spring. Will...
I had both the Triple K woodsman and Simply Rugged and kept the Triple K. The Triple K has suede linning and a thumb break, and fit better. The woodsman model covers the trigger as well. The Simply Rugged just didn't feel like it held my gun securely.
The part # is KW00403 on the .22. I'm not sure of the poundage, but I'd guess it is 17# or so.
I'm running the 10# spring in my .357 sp101, no light strikes so far. If I was using it as a carry gun I'd probably use a 12# though, just to make sure.
I don't think the internals are any different- my .357 and .22 SP101's are very similar, but rather as other posters have mentioned that the .22lr needs a stiffer spring to go bang each time. I tried the 10# and 12# wolff hammer springs but got the occasional light strike. I switched to a 14#...
It prevents the trigger and hammer from rubbing on the frame, increasing the pull weight and taking some of the hammer force away. Not necessary on all guns, but if you see drag marks on your trigger or hammer it can help prevent that contact.
I have the Wolff trigger spring in my SP101 .22 4.2", but not the hammer spring. I used the 12# hammer spring but would get occasional light strikes, typically one for every few cylinders. I put in a 14# stock .357 SP101 spring and it has gone bang every time since.
The Wolff kit fits in the newer 22 SP101's but may give light strikes if you put in the lighter hammer spring. I ended up using the Wolff trigger spring and the 14# stock spring for a SP101 .357. That some polishing and a shim kit and I now have a great trigger.