I was worried about this as well, because of Bentley's size, if it would be too invasive for him. I have a weiner dog as well as 2 cats (one lg / one sm) and they are all chipped. I just wasn't sure about Bent since he is only 6-1/2 lbs. and this was one of the questions I would forget to ask EVERY time we are at the vet.
Last visit we spoke about neutering him in another month or so. So sounds like the microchip is ok for him to do at that time too.
Thanks for sharing your experiences!
Peggy (a.k.a. Bentley's momma)