I also found 2 photos of Tusa transmitters on ebay, also prefix BM. I'm not at all sure how Huish decides to replace transmitter in their service program, perhaps it is the serial number and not the prefix.
View attachment 831563
Tusa IQ 950 Dive Computer With Air Integration | eBay
<p>Used Tusa Zen IQ 950 with air integration piece. Does not include box or extra wrist band. Light scratches due to normal wear and tear. Still works perfectly and batteries were just changed.</p>
www.ebay.com
The Zen 950 appears to be (have been) available with just the computer or bundled with a transmitter. This one has no box, so no way to see if the transmitter likely came together with the computer.
"air integration piece" doesn't give me an overwhelming sense of provenance ...