[EricH]

One final thing to consider: the driver. Can your driver handle the extra maneuverability? IF definitely not, then stick with what works. If he just needs practice, do you have the resources to build a second frame (robot would be better, though), weight it down, and practice for weeks on end? If he can handle it without extra practice, give it to him anyway if possible.

Note: during testing in 2005, we noticed that strafing ability was impaired by holding a tetra about 2' away from the drive base. We just couldn't go straight sideways. We'd arc towards the tetra.

And yes, mecanums do tend to be slower sideways than front-to-back. At least, the first iteration does. It has to do with the fact that instead of having all the rollers work together, half of them are "fighting" the other half, so the robot moves more slowly. It looks something like this:
straight: --> --> ....sideways: --> <-- ....diagonally: --> --
........... --> --> ................. <-- --> ................... -- -->