The boarding facility next door to me has one and I trailered my horse over and rode in it.
Very light and bright inside, was a pleasant temperature inside despite it being extremely cold outside.
The biggest issue is that the side supports are angled in such a fashion that while a horse can fit neatly under them, the human would be decapitated. Sooo... if you have an ancy, extremely green horse (which if course would be what I was riding) it's downright dangerous. So my trainer lined all the supports with barrels, chairs, tables, jumps.... basically anything she could find and while this served to keep him and I safe, we lost a good 4 feet of space in what was already a TINY arena.
It was incredibly dusty but I would attribute this to lack of maintenance/proper footing.
So it was *ok*... nothing wonderful, nothing worth hauling my horse over to ride in and I would definitely NOT consider buying one. They're expensive AND you lose at least 4 feet of it's width to those supports.