I bought this for my little Robo, Parsnip. I adopted him after he was returned to the store, so about 5 months old, and nearly fully grown. I can't comment on whether younger robos could try and squeeze through the bars (they're just under 1 cm apart, and most places advise bars to be 0.7cm in cages for robos, so I guess that is for the children!). He can't climb over it, although the first few times he got about 2/3 up, and also scampered around the boundaries for hours. I was a bit worried after reading all the reviews about hamsters escaping, but I work late at home, and after a week or so of his new playground, I can now get on with work, knowing he can't get out, phew. And he seems to enjoy being out for a few hours and getting treats. I'm considering getting another one for a bigger run now. Having said all this - I've only had Syrians before, and they are pretty copacetic - Robos are a little bit manic and neurotic. If you can bear the disorder in your room/study, it seems to be much better if you can leave the playpen set up, at least for a few days around the times you clean their cages. They get really stressed by too much change. I stick a few sheets of newspaper down (robos don't drink much, and newspaper is perfectly adequate and easily changed!) and leave the arrangement, and as much bedding/wood shavings as possible, seems to help him get more excited about his toys, and less freaked out by changes in his cage, etc. Plus, he spends much more time climbing on his toys, and far less time trying to climb up the bars! My syrians were all little houdinis, and robos are much faster, so it's great that I know he can't easily get out - and doesn't really have any inclination to either. I've lost him once in my room, and unlike tracking down a syrian, it took hours to get him back. (I wouldn't mind, except I'm scared to step on him, or let him get eat through all my cables...) I'd still worry if I had a young robo that he'd squeeze through - why can't this product just be made with 7mm spacings specifically for dwarf hammies? Would allow robo owners to give their pet more freedom from childhood, without having to worry every second that the little one would get stuck, or even escape. Also for people with mice, 1cm seems far too wide. This is the only reason I've given it 4, not 5, stars. Parsnip would give it 5 (and certainly will, when he gets his new toys and extension!). And for gerbils/syrians, it may well be too low (at least another 5-10cm) - for guinea pigs the height seems OK, but for Syrians and anything bigger, I think you need at least 2 if you can find the space, though the spacing of the bars seems fine for syrians. So, in conclusion - adult dwarf hammies should be fine, but one run is certainly not adequate for anything bigger; this works brilliantly for Parsnip, but really this should be available with narrower spacings for dwarf hammies/mice, and with the current spacing, but higher for gerbils etc. And if you have rats, you'll definitely need at least 2! Very glad I bought this though, gives Parsnip a lot more fun than he would get otherwise, so Robo owners: once they are more or less fully grown, I think this is safe for them, and they'll love you for it! Robo owners with babies/mouse owners: try and find something with narrower spacing (sorry :( ).
