I touched on this topic here but the basic summary for the dominance of deadwheels in FTC is that unlike FRC with blue nitrile and griplocks, FTC robots are inherently traction limited by the field damage test; even 6wd and swerve teams find themselves using deadwheels for this reason.
Optical mouse sensors for the longest time just weren’t good enough to be used for odometry (and would not track at the speeds that robots move at) but the new PixArt PAA5160 chip in the SparkFun product is the first that might start to buck that trend – it’s newer than the Pimoroni board and likely strictly better. I’m curious to see how it does on a real playing field though.