I like handling my robos when they're out, and wouldn't like the thought of them only getting to go out in the ball, so currently I use a playbox for them. My robos are too fast/not tame enough yet to take them out just in my hands.
However, I only have the one box. I only put the hamsters in it one at a time, but I'm sure some people would say they shouldn't have the same box at all, as they can then smell each other in it. But I don't really have the space for two cages and two big play boxes to be setup in my dining room, so I'm relatively satisfied with the arrangement for now.
I like playing with them while they're out, so I take the lid off the box and kneel/sit so I can rest my arms in it, so they can get used to running over me. McNulty has worked out that if he runs up my arms when they're at an angle he can get much nearer the exit, so he spends a lot of his time doing that now
It's quite a big box, and I've just started putting Carefresh as a base in it so it's a bit softer for when they jump around and fall. I usually put a dish of sand in there too - they are far more likely to use that one than the one in their cages for some reason and it's cute to see them spin round in it in close up
I've got a few items (wooden bridge/seesaw, etc) I put in there when they're alone - they seem to quite like them.
I've also ordered a metal playpen so I might try that too. I have a ball but they only use that very occasionally as I'm paranoid about them getting out.