I use the Korg KDM-2 which is an extra loud metronome for drummers with earphone jack, different click sounds (at least two acceptable ones), led indication, a tap control, up to 9/x measures and 10 different rhythm patterns ... BUT the main benefit of this metronome is that it is loud enough to being used in an ensemble.
On the other hand it can handle beats down to 30! This is important if you pratice with the metronome in the jazzy way, i.e. have it beat alla breve. Instead of being controlled every beat the metronome provides only every second beat thus forcing the player to find the right intermediate beats. This developes a nice "swinging feeling" without really (jazz) swinging, of course! This is even stronger provided the metronome plays the 2 and 4 of a 4/4 measure e.g. instead of the 1 and 3! Try it and you will be surprised how joyful practicing with a metronome can be!
Unfortunatelly the slow tempi are the weak side of the otherwise nicer mechanical metronomes. Their utimate bottom limit is 40 and they are usually very unstable in that range.