[JLambert]

If you have the time to do it, I would suggest trying the sensors out on a basic chassis. Just see how they work and see if you can get it do what you want it to do.

The problem with trying to calculate how far your robot is going is how you're measuring it. If you're counting rotations of your wheels, then it's very possible to get major errors. If your robot strikes something, and continues to go, the wheel that's being measured may spin, causing you to get innacurate information.

However, if you had an extra wheel that was not attached to any drive system, you could use that to gather your distance info. SO if you had two rear wheels for drive, using one of the front wheels, or a fifth wheel if you had four wheel drive. That way, you would know that when the drive motors are going, but that wheel isn't, you're not only not moving, but you could put code in to make the robot react appropriately.

On the other side of the coin, the sensors have their own share of problems. If you space them too close together, the robot can get jumpy as it follows it's path. And if another robot knocks you off the path, your robot could become completely useless for the first 15 seconds.

Ultimately, the choice is up to your team. It all depends on what you're going to do in autonomous mode, and which method would have the least cons.