First, the size. This is quite a large item - it has to be, to accommodate the water reservoir. So it is not really suitable for travelling (or, for that matter, for anyone with very small hands).
How well does it do its job, though? The answer is, very well - even on the standard setting, it blasts particles of food out of tooth crevices where they have lodged. And your mouth feels fresh afterwards. All very satisfying. There are a couple of reservations, though. First, the reservoir only just holds enough water for once round the mouth (though you can of course refill it in the course of a clean). A bigger problem is that the irrigator does not remove the plaque that brushing leaves. After 2-3 days use of the irrigator (but no other post-brushing steps), an interdental cleaning exercise is likely to find quite a bit of plaque. My dentist explained that the stickiness of plaque means that irrigators will not remove it, and this is indeed what I have found.
Given that this device does not provide a complete post-brushing solution, can it be recommended? Yes, provided you also have an interdental cleaning strategy for removing plaque. Oh, and if you decide to get it, be sure to follow the advice of the instructions to use tepid or warm water. Cold water will be a shock!
UPDATE - Feb 2013.
This product is even more useful than I had thought. Having recently started using the very effective TePe TePe Interdental Brush Yellow 0.7mm Pack of 8
(and a couple of other sizes), I notice that this irrigator still finds bits to remove after TePe use! So it really does deserve the full five stars.