[Nibbler]

As far as I've read, it very much depends on the hamster. Some would be far too large for the tubes whereas others use them and love them. If you've seen him go all the way through he should be fine for now. Just keep your eye on him in the future.

As long as he's got an alternate route up there he may use his own judgement (most of the time) and go with the route he feels most comfortable with. He may not use them, simply out of preference. Then again, if they're a new addition to his cage, I'd give him a while with them to see how he gets used to them.

My male Syrian could do a squished 180 degree turn in one of his straight tubes (somehow!?) when he was younger and under 120g but I've not seen him do it in at least 6 weeks (+25g later). He can still walk through them, but he now backs up if he decides he doesn't want to come out of the other end after all. He also uses them less frequently than he used to, as far as I've seen.