While I had them open, I decided to take a look at the innards of the controller to see what differences there were between a 36V 22A controller and Lyen's 72V 35A controller.
Lyen's 72V (100V max) 35A controller (notice the massive number of wires along with the huge power lines and the hot glue holding the capacitor in place)
The 36V 22A controller has a much simpler and less crowded layout inside. Both have 9 FETs but this controller's FETS are unmarked.
Both controllers side by side.
36V 22A controller on the left and Lyen's 72V 35A controller on the right. The Lyen controller's circuit board is actually a bit smaller than the 36V one!
Here's a picture of the bike with the new controller box mounted between the seat post and the rear Topeak rack.
Here's a shot of the whole bike with the new black controller. It's much less obvious than before.
The bike looks much cleaner now with the black controller. The controller now disappears into the background rather than stick out of the visual lines of my TF S-750.