I have a J-Point, which is similar to the Dr Optic, on a Glock, and it works just as I hoped it would. It was very easy to mount, it is fast and accurate and holds zero, and it has held up to over 1,000 rounds 9mm. It also weighs so little, you hardly even notice it.
I was worried about durability, because they have to withstand the slide slamming back and forth. So far with the 9mm, it has held up fine.
My next step, when I'm ready to spend the money, is to put a J-Point or Doctor on my XD 40 or Kimber 10mm, and hopefully it will hold up to the punishment.
I think the Doctor is built a little more solid than the J-Point. It is also more expensive.