I had a known fault (diagnosed for free during service) on my E39 2002. Passenger side occupancy sensor. Decided to DIY and installed the bypass module (about £15).
The Airbag light did not go out so I needed the reset tool. After some searching it seemed the only one mentioned here was the PEAKE SRS reset tool. I tried bidding on second hand ones but couldn't get one for under £80, and new ones were more still.
In the end I purchased a B200 BMW SRS scan reset tool, made in china by these guys
Bought through a popular auction site and delivered to my door for £46
The tool correctly displayed the fault code and also successfully reset the SRS light.
Comes with the newer under dash OBDII connector and the older circular one for earlier cars.
Seems like a good option for one off or infrequent use.
Just thought this feedback would be helpful.