Keys on this number pad are not full sized as advertised. They are noticeably smaller than the keys on my laptop keyboard. This makes it impossible for me to use it at anywhere near my usual speeds of about 150-200 cpm. I have uploaded a photo showing the difference between this keypad and my laptop keys. I'd guess this is to keep the entire pad small enough to prevent hands from getting sore when using as a mouse.
You can also see in the photo how the buttons overhang the top row. It looks like this would be a problem but it's not interfered with me at all while going slow enough to use.
While the key size is a big disappointment, it's the only one. So I am keeping it since it works well if I don't try to work by touch. It is still much easier to use than the integrated keypad on the laptop keyboard. Backspace key on the top row is very nice to have, that's for sure.