Can't vouch for the Yaris specifically ... but on our original 04 Corolla, we had cruise fitted. Its the same model that Autobarn sells for around $400-$500, we had the one with a stalk control, but for a bit more you can have button controls that fit on the steering wheel. Anyway, we found it excellent, its not 100% as intuitive as a factory-fit system, but I'd say its 97 or 98% there, you only notice the difference if you drive the two styles back-to-back, I found. I credit it with our best highway mileage, an auto Corolla wagon, fully loaded, air con on max on a 31 degree Xmas Eve, sitting on the speed limit between Brisbane and Hervey Bay (about 3.5 hours each way) and we averaged just under 7 litres per 100km for the trip. The cruise just moderates the throttle more accurately than humans can. The Yaris has similar engine technology to the Rolla, so it should be pretty similar. Hope that helps!