[apalrd]

Look for a potentiometer or absolute encoder with analog output.

We've used standard 1,3,5,10 turn pots for things like this (anything 10k to 100k will work). We've also used US Digital MA3 magnetic absolute encoders, those are nice as well.

Relative encoders (such as the quadrature encoders in the kit) are not absolute. They can tell you how far you have gone, and how fast you are going, and what direction, but cannot give you any zero position reference. For a swerve, since you don't know where the pods are when you boot up or if they ever move when you are powered off or reboot, you would like an absolute sensor like a potentiometer.

Building a swerve is hard. Don't underestimate how hard it is. Also don't overestimate how much benefit you will get. Mounting a sensor to the swerve pods is part of the many mechanical design challanges you will encounter while building a swerve drive. One method of mounting the sensor is to make it inline with the steering chain.