I should have added this information to the post above. Obviously, the Tweels I have are not the drive wheels, they are rear casters 13x6.5x6.
They do gather mud in the webbing when conditions exist. I would take a stick and dig out the mud, not an immense amount, out of the webbing. I later found that once the mud dries, it quickly breaks out of the webbing as the Tweel flexes. A google shows the current price of $238 per Tweel and I paid far less for my pair from a local dealer. I could have purchased foam filled casters at a less cost but I have found that they do not last that long.
I would not recommend Tweels for the homeowner mower. The expense to repair a pneumatic tire compared running Tweels is a no brainer. However, a commercial mower, the time lost due to a flat is lost revenue.
Would I buy Tweels again? I have three other commercial mowers and they do not have Tweels. A cheaper alternative is to have a spare tire and wheel ready to replace a flat and address the repair at my leisure. I would never consider putting them on my automobiles.