I don't know much about aftermarket OBD-II scanners. I don't have one worth anything at this point. I was looking at Techstream light (by Toyota) but that would be for work and could justify the $450 price tag. For the average person to use it would not be very cost effective.
As far as being able to "tune" a Toyota ECU, good luck. Toyota never released the information (language) to the pubic market. No aftermarket programmers can reflash a Toyota ECU at this time other then to install factory programs. Fuel and timing maps can not be changed by the end user at this point. This is why URD and other piggy backs are popular.