I had a UAG for my SP3 and loved it so also got one for my SP4.
Haven't used it that much but initial impressions are great. The type cover fits perfectly over the screen and an elastic holder keeps it in place. It is sturdy enough to throw on the front seat of the car or in a bag and still protect the device. My only gripe is that the pull out stand has a lot of free movement in each setting unlike the device stand which stays in place.
The fit is snug but I can't see how it could possibly crack the screen unless you did it while putting it into or taking it out of the case. I usually insert mine into the case from the bottom up so it slides into the top part and then gentle lift each bottom corner over the device. With the cut out for the type cover it means you can move it away from the corner while lifting it over if that makes sense.