CPT-20 works well. Screen turns green and stays green when string is in tune. If it won't stay green, it's the string, not CPT-20.
I have about five Thomann CTG-10 Clip tuners, so the screen was quite familiar. I consider CPT-20 like a CTG-10 in the pedal form. Nothing bad about it. I can still see the screen w/o my glasses while standing. Just about.
I also have a few Thomann CTC-50 Red tuners in my concert guitars cases. I find CTC-50 superior to CTG-10. I also have a Behringer rack tuner, which works well. The rack tuner is plugged into the recording out of my M/B Quad preamp, so I can't mute while tuning. That can be annoying playing live. I only use it during concerts if there is no other way. With clip tuners I can tune in silence, but I like to have another option for tuning in silence on the pedal board.
So I was looking for a cheap tuner/mute button with a small footprint to save precious space on PB. And CPT-20 would actually be a great choice if only a bit more attention was paid to details. The power input is like really loose, it moves into all directions. Not just a bit, more like 2 mm wiggle room. Also the switch feels cheap. It's also just a bit low, I used a S-Connector between a small buffer pedal and the CPT-20 and it's not a perfect match. The absence of battery does not bother me at all. The thing I really like was the brushed aluminum face of the pedal. More pedals should be like that.
All in all, could be made better. But it works. We'll see how long.
