I put a set on a Colt that I had redone a couple of years ago. I was sceptical at first because I'd heard that the sights sometimes presented varied learning curves to operators.
I use the gun strictly as a SD weapon in the nightstand. You are right about the quick target acquisitiion and I've found that they really do a good job in the low light conditions that you'd expect to find where I keep the gun.
I had very little difficulty in getting aclimated to the XS system. They aren't target sights but...
Bottom line-I like them for what I got them for.
Here's a picture of them installed on the Colt I had redone: