I don't like the 40 series tires/wheels on the track, but for bashing and just plain looks, they are nice; although they are tough on the drive train.

The 23mm hexes are nice and look tough, but they do limit your choice of wheels. If you want to race, you really need to go with a wheel that will accommodate the MTR series of tires. They work very well on the track. For the MTR size tires, you don't need the 23mm hexes, although I can see their benefit when running the larger 40 series tires.