Whether you go unsensored or not depends entirely on reduction. If you're going for a single-stage like with those Alienpower outrunners, sensored is a must have (and even then it hasn't proven itself yet) but if you go for a fast inrunner with a bigger reduction, such as 36:1 from drill gearboxes, you'll be able to get away without sensored motors. It's nice to have, but from what I can gather not essential with that much of a reduction.