I'm a pro drummer and teacher and this metronome is everything I could ever want in such an item. It is very easy to use and comes with a huge variety of options - not only can you set any number of beats per bar from 0 to 7, but you can also very quickly set the metronome to subdivide into quavers, semiquavers or triplets, a triplet shuffle or a semiquaver 'samba' ('1' and 'a' of a 1e+a set of semiquavers).
You can also tap a tempo in yourself, and the metronome will pick up how fast you're playing, which I have found incredibly useful when wanting to get quick a reference in the studio.
You can also mute the metronome at the touch of a button; again this is great for the studio as it leaves the digital display showing a side to side animation, just like an old fashioned classical metronome, which is much easier to follow than just a flashing light, but obviously won't be picked up by any mikes.
Finally, unlike some other cheap metronomes which raise the tempo in steps, this metronome can be set to any BPM number from 40 to 208, great for teasing the speed up in practise sessions.
By the way, I never use it but there's a tuning note feature which you can set to any tuning note, and also calibrate the exact pitch of each note. This thing has stuff I don't even use!
A few people have said it's tricky to use, and while I admit that I've fumbled over the buttons a couple of times as some of them perform various tasks, it's never really taken me more than a moment to get the thing to do what I want. The only thing it doesn't allow is programming time signature changes in, but the only metronomes I've seen that can do this cost hundreds of pounds. It's small, it's portable, it lives in my stick bag and is always there when I need it. And yes, it's kinda quiet (I always have it set to full volume) but you can always stick a pair of headphones in and you're away. I've used it on some noisy big band sessions and haven't had a problem, and to be honest the fact that you can adjust the volume at all is impressive given the price. I couldn't recommend this product enough - even if it does go 'beep' instead of 'click'. I honestly don't think you'll find a more functional product at this price.