TireBalls in my opinion are the best thing ever made for a quad. Once you have ridden with them you will never want to go back to air tires. Yes they are expensive but worth every penny if you don't like dealing with flat tires. If I had to race a stock quad and was only able to add one thing, TireBalls would be the thing I would pick first.
Not only do they help with the flats issue but they also help with the ride/handling and traction of the quad. Because there are so many balls in the tires, you can run a lower pressure. This helps smooth out the ride and allows the tires to grab the ground more.
They are also very durable. At the Baja 500 this year on my first day of prerunning, I slid around a corner too fast right into a boulder pile. I ended up with about a 4" L shaped gash cut all the way through the sidewall of my rear tire. I continued prerunning my quad at race speeds over 100 miles each day for the whole week before the race and never changed the tire.
To give you an idea how much I like them, I've only bought two things for my quad. Houser a-arms and TireBalls. And if you don't think that sounds crazy, just ask Wayne how much I like spending money!