The 12" Silent Runner attached to the bars is great! I've used it like that for over a year and it's a safe and sturdy wheel. I would take the 12" Silent runner back and get a refund - they're huge (deep) and apparently don't spin that well any more since a manufacturing change. I love my silent runner attached to the bars, because you can have the wheel right up near the top of the cage (so the hamster can't climb on top of it) and have space for lots of substrate underneath it.
The Silent runner is 9cm deep as opposed to the silent runner which is 13cm deep so really bulky. The silent runner is actually silent as well
And spins really well and is easy for them to run in.