Wahoos' Fitness app is part of the Wahoo ecosystem, so as far as I know it will require one of their trackers to work. However, it makes big sense to use one of their heart rate belts because it enables you to have heart rate included to your workouts with your cellphone or actually accurate heart rate added to your workouts with the apple watch. If using the Tickr X, you don't even need any other device as your workout is saved directly on the HR-belt, which is pretty awesome if you ask me.
Pro Shows you an overview of all trainings
The app will also show you an overview of all your trainings telling you how many calories you have burned in your workouts, how many trainings you have logged, how many Kilometers (or miles) you have ran and how many hours you have spent working out. It is, of course, also possible to go into all your previous workouts and look at all the exact details of every single one of them, if you would like.
Pro Syncs with Apple's health app
The app syncs well with apple health and you get all your logged activities and data transferred. It will even track the Nike Fuel points, but those will not sync over to Apple's health app because in there the Wahoo app can not be selected as a source.
Pro Can select other heart rate monitors
I once had on my Wahoo Tickr X and a Basis Peek smartwatch and it gave me the option which of the HR-motiros I wanted to take the heart rate from. I never attempted to use the Basis as the Tickr is much more accurate, but I would assume it lets you use any BT HR-tracker that is around to connect. This may mean the app could also work without a Wahoo device, but I am not sure and it would certainly loose you a lot of the other PROs
Pro Can track workouts in the gym
The app does not only work for running or cycling outdoors, but also for running on a treadmill where it will also measure your distance and pace based on calculations it makes after you set it up and for indoor cycling (or spinning) where it will measure your cadence (but not distance) quite accurately. It will also let you track a weight lifting session and will then tell you about how many calories you burned. This is another feature not many other trackers have. Most of the functions will only work with their top of the line Tickr X for about USD 100, but the basics are also available with the base model.
Con Many apps, slightly confusing
Wahoo offers several apps and in one case this can be confusing. This review is about the Wahoo Fitness app, but they also offer a similar one which is the Wahoo RunFit app and this does not track half of the stuff. I don't see why it even exists as it can only do less the the Fitness app. They offer several other apps as well which I have not looked at so far, but they do other things entirely as far as I could tell and thus do not create more confusion.
Con Relatively high buy in
You need a Wahoo product to use the app, the buy-in to get the app is relatively high starting at about USD 50 and going up very much higher depending on what equipment from them you choose. For some, it might well be worth the investment of USD 100 for the Tickr X, but it is surely not for everyone!