I have a Garmin 920XT multisport watch. It does running, swimming, and cycling. ANT communications with HR monitor (strap around chest - I think pretty accurate) and with an ANT USB mini-dongle. It communicates with the Bontrager duotrap to get speed and cadence. Gives me an accurate map of my ride, and the Garmin Connnect Web-based software is ok (a little inflexible and obtrusive, but ok).

If you are interested in logging your workout, cadence, speed, (and watts, too, I think, if my bike had a power meter), a watch is fine. If you like to be able to look down and see current speed, or power, or where you are on a map, a watch is not optimal unless you have young eyes that will adjust from road to short distance quickly.

There are more modern versions of the Garmin watch-based multisport thingie I think. Garmin support has been very good.