Actually I've been using the RL500 as my only lawnmower for 3 years. I KNOW it works and it works very well. My yard is over 15,000 sqft with flower beds and trees just like any other yard. The only problem they have is with slopes. If the slope is over 20 degrees, it'll slip. Other than that, these mowers are very smart and manage the cut the grass making it look better than when I used to cut the old fashion way with a push mower. They're already many thousand that have sold in the US...in fact search for robomower on ebay you'll see many used ones for sale.
Check out the website here at:
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for info and videos as to how they work. I was skeptical too when I first tried mine. Now I'll never mow the old fashion way again.
Robomower forums: forums.robomower.biz
forums.robomower.biz to discuss automatic lawnmower