Check out the latest user manual (text in orange) ...
http://crosstheroadelectronics.com/T...Manual_1_3.pdf
...or andymark...
http://www.andymark.com/Talon-p/am-2505.htm
...for the details but basically Talon SRs are more efficient at stall (less heat), expanding the no-fan usecase. Also the led blink pattern is more distinct between Full throttle (full forward/reverse - led solid) and "Less then full" throttle (99.999% in either direction - led blink). Led blink rate still indicates magnitude though (just like before).