Switcheasy Numbers fits the 6S but there is less space above the bevel around the screen since the 6s is thicker than the 6. With my 6 I use the numbers case along with the invisibleshield glass screen protector and the case goes above the screen protector (so that when you put the phone face down the case is touching the table rather than the screen protector). I think that with the old numbers case and the 6S the screen protector would touch the table (haven't tried it, going without a screen protector for the time being).
HOWEVER...Switcheasy seems to have updated their site now and have a NEW version of the numbers case along with another new case specifically for the 6S. So hopefully those are better because I really like the way this combination works on my 6.