That is really all you need to know. It works, you're just gonna use this to protect your lens and that is all that matters.
It does what a UV filter is primarily meant to do - protect the lens. Although you have to be very steady-handed to thread it on the lens properly, that's a minor inconvenience that you won't have to deal with very often. It doesn't interfere with the picture at all even at the wide (27mm) angle setting of my camera. If it does what other UV filters do for a lot lower cost, why wouldn't it deserve a top rating?