Took first long paddle with app and used the watch app to log the trip. When I tried to start logging, it kept telling me to enable workouts in the iPhone Health app, which I had done. I even turned them off and back on again, but the watch app kept posting these same alerts, until it suddenly started tracking. Noticed that it didn't seem to sync with the phone app while running, which concerned me.
Kayaked about 3 hours and went to stop the logging but got an error saying it couldn't save my trip! Then I couldn't stop it: tapping on Stop did nothing. Could still tap on the Mark button, but not Stop. Had to turn the watch off and back on to get PaddleLogger to stop tracking.
The phone app seems fine, but the watch app was enormously frustrating.
UPDATE: Tried using just the iPhone app the next day. Not much better experience. PaddleLogger recorded the trip time and length, but the map didn't record the full trip: kayaked up a river and back, but the map shows that the trip ended about 2/3 of the trip up. Additionally, the Health app says there wasn't enough heartbeat data to record anything (after an hour!). Finally, even the incomplete map wasn't shown in the Activity app. So in summary, nothing worked in back to back sessions. One star.