I have got 2 of these for my 2year old, one at grandma's and one at mine.
Such a good idea. No other mess. The pens fill with water. My daughter first got hers aged 1... and no, that wasn't too early! She has loved it ever since.
They aren't perfect,but what is? the mats are susceptible to dirt, as are the pens. I read a couple of review from mums who didn't like them as their children threw juice over them or got the pens dirty, but seriously, keep other liquids away from your children whilst they are being played with, and the pens away when they aren't being used, and whats the problem?
These are with no doubt one of the best toys my daughter has ever had and I already have one in my basket as a Christmas present for another child.
oh... and because they fold up, they are great to take away with you too, great for trains, they cover the whole table! You can even get a travel one which is good for cars.