We bought this for our ant-obsessed son, and the whole family and all visitors have loved watching the ants work.
A couple of notes:
The life-span of the ants is about 3 months -- it's been exactly 3 months and we have about 4 living ants left.
The ants bite - at a science store where we bought the habitat, they had one on display. The cashier was trying to show me how you would clean out any dead ants, and when he lifted the lid, the ants swarmed out and a few bit him. I taped the lid shut to deter any kids from trying to open it.
If you refrigerate the habitat for 15 minutes, that will make the ants sluggish, and you can clean out any dead ants or excess gel that the ants bring to the surface. However, set a timer! Once I left the poor ants in the refrigerator for 2 hours and when I retrieved them they were all huddled at the bottom of the habitat. Fortunately, they all survived (although perhaps you should take the 3 month life-span with a grain of salt, given the extreme conditions they faced early in their habitat life).
Due to health and mortality concerns, my son would not allow me to put a drop of nail polish on the back of one ant so that we could name him and chart his/her progress. I think that would have made the habitat even more interesting, to be able to track one specific ant.
Also, the clerk at the science store said the gel is reusable, that is, when the old ants all die, I can add more ants. That would also be interesting - would they close off the old tunnels and build new ones? Would they use the ones that exist? Too bad I've misplaced the order form...
All in all, a very worthwhile $20.