Well, class III lasers are strong enough that you *should* be careful when using them, they can definitely cause damage to your eyes if you look directly at the laser or a clear reflection of the laser. Personally I've never never seen/heard of anyone getting hurt by one, basic awareness of the threat and simple precautions (be aware of any mirrors in the room where you're using the level etc) are probably sufficient. If you want to really be safe, you can buy Laser Safety glasses from Amazon at varying prices.
For details on the class levels you can see a
breakdown on Arizona State U's site.
I would take a second look at the particular model you linked to there though, there's only one review on Amazon, but it's not exactly heaped with praise

.
James