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.