Martin,
I can't tell what you do and don't know about Teledyne sensors, but your instructor should have explained all of these clearly so you could make an informed choice.
Real brief summary:
- Both R22BUD-2 (sold by APD) and R22D (sold by different sources, mainly from Oxycheq) are both manufactured by Teledyne.
- You could only buy R22BUD-2 from APD, AFAIK, since they were made specifically for APD.
The rest of the differences, you should be able to get from this
LINK.
There are some links within the Oxycheq website discussing about the difference between Teledyne sensors and others. Take a look...
Personally, I use both interchangeably but I don't want to influence anyone's choice regarding which one to use. So I just direct you to the sites giving the information, and you make your own decision.
You could also ask your instructor for recommendation.