"jocala, does it take a lot of time deciding to switch notes? I've got a Planet Waves tuner (PW-CT-07) and it tends to stick to the last note - though that's when using the internal microphone with an acoustic guitar, it might be more responsive via line-in. Did you own a Theremini at one point?"
I started with a Theremini and sent it back after a week. I found that the internal speaker did quite a bit of buzzing at loud volumes.
The TM-50 response seems pretty fast to me. It moves instantly when I move my hand. I don't notice any stalling or sticking.
I'm just using the internal mic, it does have an 1/4 input jack, but I haven't used it. You can see the user's manual here:
https://goo.gl/nsf3q5
Edit: I find that when playing quickly, this tuner does lag a bit.