I had one and used it quite a bit.
Here were the pros:
--My son had a place to stand and ride when he was tired of walking, so I didn't have to hear the complaining of "I'm tired of walking."
--It was easy to hook up and out of the way when he actually was walking and not riding.
--You could take it off and have your regular stroller again.
Here were the cons:
--It was quite tricky to get the connectors on the right place on the stroller.
--I had to unhook it from the stroller (umbrella style) to fold up the stroller for the trunk. Not terrible, but not convenient either.
--It is a bit awkward to push the stroller with the child riding on the board because that's where your feet need to go. It's not impossible, you just have to adjust how you push the stroller, either streching your arms out farther in front, taking shorter steps, or walking kind of to the side.
All in all, I would get it again if it wasn't too expensive. Maybe look for a discounted one on eBay?
However, about fitting it on a Maclaren... My stroller was a Kolcraft which had round tubes and the connectors worked fine. When we were finished with it I gave it to a friend who had a Maclaren. Her stroller had square tubes, and she had a very hard time getting the connectors tight enough so they wouldn't slip. She ended up not getting it to work. But this could have something to do with the connectors already having been used once. And also, they may have made improvements in the last few years.
Perhaps someone with a newer model and a Maclaren will be able to tell you how theirs is working...