Works for most metric conversions. Would like metric to imperial as well.

I see it functioning inline (I literally just installed it a minute ago and loaded up a page) which is exactly what I expected and wanted, so I thought I'd give feedback.
This is a great start (and finish, if you're a busy dev) but it could be improved in a couple of ways. It would be nice to see the original value and then the converted value afterwards in parenthesis. Also, it would be nice to be able to adjust precision. The value I'm seeing was 31 mph, which the plugin says is 49.92 km/h which is coo but 49.9 would probably be fine for me and maybe for others, 50. I dunno. These would be nice touches but not essential.
I might update this if there are glitches in the future but for now, excellent plugin and I definitely recommend it.

Too experimental, can't find it and therefore cannot figure out how to make it work Hope the developer keeps working on it, great idea that could be useful

Fairly consistently picks up and converts units, though can miss due to formatting.

Would be nice to be able to see the original as well, or at least distinguish when a conversion occurred.

It's pretty useful for the units it provides. It would be incredible if more units / currency were supported, and that there was a way to tell if the unit was converted or not (a different color, maybe).

please add length

Thank you for the effort - looks promising. I hope we will eventually see more units supported.

If you are looking for inspiration: years ago another really nice guy (*) developed an extension named Converter, that worked really fine. In 2015 he ended development and released the code as Open Source - you can find it here https://github.com/Gutza/Converter

(*) in 2011 the extension stopped working after an update; for the first time I emailed the developer of an extension I used. The next day the issue was already fixed, and we exchanged some really nice emails - he was a great guy!