a few months ago I got night sites for my new 30S since I like them so well on model 21..... back then they did not list 30S so I assumed (yes I know) since the 30S has the 36 slide to pick that one (along with advice from various dealers selling them). NOT.
It took me a while to figure out why I couln't hit a target at 20 feet with them; model 36 sites point gun down about 2-3" at only 20 feet.
Just checked and XS now lists the 30S and it is the same model as the 21 - not the different 36.
Just a heads up for anyone else embarking on same trek - it will probably take some time yet for all the distributors to realize it is not the model 36 ones.