I've mentioned this before, but at least my Landroid manages hills and slopes well. However, there's a couple of things you need to do in order to avoid issues. If your grass is already tall, your robot might get stuck when trying to go uphill. In case the hill is close to the border of your lawn, the robot might (quite comically) just slide off the lot and freeze. These, and all other problems, are made worse when it's wet outside! And obviously, different devices will have different maximum grades they can navigate. Some AWD models claim they can do over 40 degrees!