I think the Jumbo (
not less than 15" in diameter) plastic ball can be safe ...
IF ...
(1) you use them for approximately 5 to 15 minutes {while considering, the amount of time depends on room temperature, never use them outside, the current health of the chin, the amount of activity and safety + keep them under
constant supervision while in the ball} ...
(2) you clean them thoroughly, before and after each use, by each chinchilla ... never use it outside, or in a room with open doors, or in the same room that has a door directly to the outside, or around steps, or in a room that has floor vents, or have furniture you can roll it under and/or where it can get it stuck in one place ... (That's a big bunch of "if"s.)
(3) Most important of all ... ONLY under close
constant supervision without distractions.
Personally, I prefer not to use them at all, now, but I use to love it.
I had one, many years ago, one of my chins loved it, but when I saw how quickly he learned how to 'pop it open' and escape, by getting it going very fast, then banging it against the furnature to pop it open. That's when the ball went 'bye-bye'.
There are pros and cons for almost anything. We just have to decide, with intelligent input and often with experience, what is best for us to do.
People only know what they experience themselves or know from others ... this vet could have seen something, or a number of very bad things, happen to chinchillas whose irresponsible owners misused the balls.
Jo Ann