Some massagers just vibrate- but not this one. This kind is known as a percussion massager, because it percusses, or "beats" on your muscles- so know that first before you buy it. Might be good to try one out in a store first if you're able to- there can be big differences between types of massagers.
For this type of massager, know that using it does require a certain amount of effort as you're going to have to hold on to it (as opposed to massage cushions and such). It may be heavy for some, I say that because most of the weight of the massager is on one end- which may make it a bit top heavy for some.
It comes with four massage balls you take one and off- three have varying firmnesses, which is nice, and the fourth set of balls heat up. Note that some people have complained that the heated balls take a little while to heat up (a matter of mins).
As percussion massagers go, this would be a good pick. A lot of people will likely use if for their back pain, which it's well suited for, particularly because the two balls are spaced wide enough apart that they fit nicely on either side of the spine. Back pain sufferers might also want to check out
Treat Your Own Spinal Stenosis.