I’m using a Sigma BC906.
But I’ve cut the wire and resoldered it with some phonecable (used with RJ11-plugs normaly).
I found that that was the easiest. But the sigma is coming loose from time to time, and mostly on the train and I hate it.
And also today I managed to brake of my rear light when pushing the bike between the trainseats, aaarrrrggghhh. Just bought some small cheap led-lights. Probably going to get the Philips Saferide to replace the stock reflector.
Also on order is the Abus Combiflex Pro lock