I'm not really at legal speed, so my controller are all 12 FETs
It's quite a big controller and difficult to hide. For now I kept it on the bag and try not to drag too much current. I'm still thinking about what you guys saying and put the controller outside the bag. I may put it under the bag but I'm not sure yet.
Here's my bike:
You can see the controller and all the wires coming out of the rear bag of the bike
I tried initially to put the controller on the frame, as it has the same colour as my brompton, but it was way too noticeable. Everybody was asking about my electric bike