Nice job on the research and post.
Do you really need one?
One alternative that is sometimes used, is to go to an Autozone or similar outfit and ask to have codes read which they have been doing for free. That option would be for infrequent use, and in fact the check engine lights come on pretty infrequently as it is. A good relation with your local Volvo specialist works well for this too. I have a 97 850 that needs a separate device (about $170) to reset the service light. I could never bring myself to get two devices, and have managed to live without them for 7 years. One caution, I went to a local import shop and he bogusly said oxygen sensors, I said 'let's try clearing the code and I'll come right back if it pops up again' I think I've had a CEL twice -one was when I got the plugs wet cleaning the engine, the other might have been the gas cap I don't remember but they were nothing major
Have fun
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'97 855na, Mobil 1, K&N, various IPD's and eBay's