I think they are a bit risky too - we had one and I took it out again. They only have to catch a foot in one of the rings and jump and your ham could be hanging by a broken leg - there have been accidents. They look cool but I think there are better roof toys and climbing toys that don't have chains and rings and are safer. In the end I went with the rat sized sputnik, a vine branch which sits on the floor of the cage and extends up the side, and a cardboard rat tube tied to the roof of the cage, which leads to the sputnik at one end and the house roof at the other end. This gives our hamster a good roof run and he loves sitting in his rat sputnik. I lined it with a circle of hemp mat to make it cosy like a hammock.
I got our vine branch from Rodipet in Germany because they do 30cm ones - a lot of the ones on Amazon are huge! Or you could just have a large bendy stick ladder/bridge instead.
The rat sputniks you can get from ratrations or here
http://www.amazon.co.uk/Nobby-Sputni...ds=rat+sputnik
The tube is a boredom breaker one with four holes punched in the top and tied up with sisal string (or you can use 'paper string') which is safe. It's the 10cm diameter medium rat tube.
Boredom Breaker Rat Medium Tube: Amazon.co.uk: Pet Supplies
Not that that's the only way, just saying you can make climbing and hanging runs with safer cage accessories. Cork tunnels and tubes are good too - they are quite big and on the floor of the cage would give height access to a sputnik and something to run under as well.
http://www.amazon.co.uk/Trixie-76400...ds=cork+tunnel
Anything cork or wood like vine branches could do to be put in the freezer for a couple of days before using in case there is anything microscopic living in them.
Anyway - this is how Charlie's cage looks. The vine branch is in the left corner and he likes to climb it and sit under it - it gives access to one side of the sputnik.
Before and after the roof tube was put in