I first bought a Glow Bee when they came out but after much frustration I bought a TNC some years ago. It is in a drawer somewhere around here. I don't really need one. I can tell how the engine is running without a tach.

The TNC works great I just don't use a tach anymore.

Before I bought the Glow Bee I used a Vibra Tach and it's on a shelf somewhere around here too.