Sorry for the crap pictures... The black dot on the cap represents the magnet(s), the white is the hall effect in the head. The head is a Ferei bicycle light head sealed for SCUBA. It has a Cree XML in 16mm format with a Kaidomain driver. Very small 3 mode driver.
I am working on another Ferei build using the Ferei W150 I showed a while back.
Yes, and yes... The reason I wanted it in the canister was 2 fold: 1. If you have the light with you, you have the magnet with you! There is no removeble part that houses the magnet that you could leave home. You'll be stuck removing your car speakers to power your dive light if you forget the goodman. 2. Environmental reason- the magnet is in a waterproof environment and will not corrode.
It does take a bit of getting used to but once you get it it's good. Now, you can also put a magnet on the goodman and have 2 magnetic triggers.
I think that torch is no longer in production. There was a guy on scubaboard selling them for bike use. You can try the Ferei W150 though. That one is already a dive light so tested to 150 meters (yes, Pack meters!).
As for multi-mode- I always dive with my light at full power so I don't necessarily think switching modes is that big of a deal. At least not to me!