I never wanted one with dd1 (thought they were overrated and a bit creepy), didn't much this time either but dh did - and I was persuaded as had potential placenta problems and was anxious about waiting till official 34 week scan to know if they'd resolved themselves.
Ended up genuinely enjoying it, felt like the first time I'd had a decent scan all pregnancy (the others were very rushed), sorted my worries, and wasn't a bit creepy when it was happening. Just interesting, and got to see dd2 moving her hands in exactly the same way dd1 did when she came out of the womb....amazing.
I don't think I'd have had it, if I hadn't had a need other than looking at my baby, but as it was - am a reluctant convert