The following are some comments on the Garmin Vivoactive for Surfski paddling. I am an intermediate paddler with no industry affiliations. This product was released in 2015, and I couldn't find a lot of info regarding its use on surfskis. Hopefully other prospective purchasers find this helpful!
I wanted a simple GPS watch that I could mount on the foot strap of my ski and pair with a chest-strap heart rate monitor. I wanted to be able to see speed in real time as well. The old Garmin 310XT is no longer sold in NZ, and its successor (the 910XT) is fairly pricey. The Vivoactive is considerably cheaper.
Getting started with the watch and heart rate monitor was somewhat complex and required a fair amount of googling to answer questions that were not covered by the manual. Once the setup was finished though everything is seamless. The watch syncs automatically with a smartphone via Bluetooth, and exercise data is uploaded to Garmin Connect automatically. You can set it up to link automatically to your Strava account. The smartphone app allows you to download apps/widgets etc to your phone.
The screen displays beautifully in the sunlight. Although it has a light that you can turn on the default is to have no backlight on (like a Kindle e-reader). This means the display is pretty dim inside (lots of complaining on the internet about this!); however outside in the bright light it is much better. I have no problems reading the data when the watch is on my Surfski foot strap. It also fits on the footstrap perfectly with no other padding or mounts needed.
I am using an app called 'Workout Genius' that lets you have between 1 and 9 data fields on the screen at once. I am using 5 - speed, heart rate, distance, elapsed time, and clock. This app, plus the built in ones for running/cycling etc are all customisable; for example you can set the screen to automatically scroll between different displays. You can (apparently) also pair it with a Vaaka cadence sensor to measure your stroke rate etc.
Options for specific training programs with intervals etc are pretty limited. So far the only way I have found to do intervals is to set walk/run interval times in the built-in running app. It is possible that future apps will give more options here, or you can buy one of the more expensive Garmins which (apparently) have more of this sort of thing. Currently there is not a specific Surfski or kayak app available either. Hopefully someone will take this on!
The watch has a couple of useful safety features too. You can download and display a compass. There a a couple of mapping/navigation apps, although they are very basic and if you need a serious ocean navigation tool this is watch is NOT it! There is a live tracking feature so family/friends on shore can see where you are in real time.
Battery life seems pretty good, after a 90 minute paddle it still had 80% power left.
It also has a lot of 'fitness watch' features which I won't go into because I am unlikely to use them. Sleep data recording, measuring steps etc etc...
For Surfski paddling though it is exactly what I wanted and the price was very reasonable. The screen visibility in particular when mounted in the ski was much better than I was expecting and for me is the best feature of the watch.
Should the watch prove to be unreliable I will post an update here, at this point though I am delighted with it and would certainly recommend it to other paddlers.