I needed this for a loft being converted into a bedroom as I was running cat5e cable from my server room to the new bedroom, as wifi signal would have been poor up there.
It does the job and is of good build quality, there is even space for a second keystone by removing the two blank fillers to the sides of the included keystone.
I only gave it four stars as the included screws were very small and did not reach into the metal back plate I was using to mount it. How ever luckily I had some longer screws lying around so it was not too much trouble, it takes two of the same type of screws you would use to mount power outlets.
BTW note to other people looking to install Ethernet outlets, you will need a punch-down tool in order to "punch down" the Ethernet cable cores into the terminals on the back of the keystone.
If you do not know if to use A or B wiring I would say just use B as most equipment uses that standard now, the worst that can happen if you get it wrong is that your network devices will not be able to communicate.