Hi John:
I've never used a KR timer, so I was unaware that it doesn't have a retract function. Will Hubin does make a twin timer with retract function. In fact, he sent me the first one (well, at least to my knowledge it was the first one...) to use in the big twin test bed model that Buddy Wieder and I built to test out motors and retracts. When we were ready to fly it, Will flew in from Ohio in his private plane to the airport that is about a mile from my house. He wanted to see it fly and make sure the retract and twin functions worked as planned. They did! In fact, in all the time we used that timer system we never had a malfunction. I used it in my Second Wind twin, and Buddy used it in his Ryan's Evil Twin model. I wouldn't even consider switching from that timer now except for the fact that it isn't an active timer. I've become so used to being able to dial in the boost and brake aspects of the Fiorotti to suit my needs that I don't think I'd be happy with any other system. And, yes the Fiorotti has a retract function as well, and each motor is able to be set for RPM independently, as was the case with the Hubin timer. To be fair here I must also mention the Igor Burger timer. It too has the retract function and independently adjustable RPM settings for each motor.
I'm pretty sure the Talon 25 ESCs will work with the E-Flite Park 450 motors in the small, light new twin, but only time and testing can prove that out. Going to the Talon 35 ESCs from the get go may be the safer bet; I'll think on that... Im sure my power system gurus, Will DeMauro and Dean Pappas will give me lots of input on this.
Attached for your reference are a couple of photos of the twins that Buddy and I have built and flown that had the Hubin twin/retract function timer on board. In fact, Will Hubin took the in-flight shots of the test bed model.
There will be lots more to come on this new project, so stay tuned.
Later - Bob