I have an older Matrix MR 500. It works fine, is adjustable from 40 to 208 BPM. It also has a light, a mute switch and a headphone jack. And it’s fairly cheap!
The problem for me is, I have a very hard time following any metronome. It’s not as easy as some would think. If you or anyone else has this same problem, what I would suggest is downloading rhythm tracks or using a drum machine. The latter may not be best for bluegrass or banjo but it may be worth a try. It makes a world of difference (for me at least).
The drum machine or rhythm tracks prove to be much more melodic and interesting and it’s a little more like being in an actual band situation. The problem however, is that it’s not as convenient as a simple metronome.
I like what Mike said about the mechanical metronome and that the uneven tempo forces him to listen more attentively. I can see how this would be good ear training.
Anyway, it’s just a thought and may or may not work for you. You could also use Ben’s rhythm tracks at the end of his lessons depending on which songs you are trying to learn.
Hmmmm, all this has got me thinking… I wonder if anyone has created a mandolin “chop” app that you could use for timing exercises?!