Lol - they are big aren't they! It's the depth really. Somehow it doesn't seem so big once it's in the cage - I've got used to it. At least you have the height for it in the Barney! I only have a couple of centimetres above and below it in our cage.
The comfort wheels come in 12" and 8.5" I think. Some people seem happy with them and others say they are noisy and break quickly.
Superpet Comfort Wheel, 12-inch, Giant: Amazon.co.uk: Pet Supplies
What colour is your Wobust wheel? I had no choice in colour as ordered as a bit of an emergency from petplanet so it is pale blue and white which somehow makes it look even bigger lol. The dark coloured ones seem to be less obtrusive.
Here's Charlie running in his - he loves it!
https://www.youtube.com/watch?v=bskSjSx3NHU