I have an integy (I think) wheelie bar in blue alum that has those small wheels that use oring like those do - its not very good - those wheels tend to catch in grass and other stuff where I run. I don't think they'd be that good on pavement either - too much wear, though I've never tried it on the pavement. It was a disappointment for as much as I paid for it.

I tried the trx wheelie bar on a lark and find it to be a lot better - especially with the bigger wheels.

in my opinion these are my favorite and reasonably prices

http://www.mdfrcwheeliebars.com/servlet/Detail?no=23

I have purchased several of the spurrs style wheelie bars. However if you cartwheel accidentally they are prone to damage as they stick out a lot. They are very strong but will take a lot of force due to the positioning on the bumper.