It's not recommended to use asensei with more than one device as you may see less accurate goals and predictions made for you. While your account history and your Up Next workout will all sync nicely across multiple devices your workout, the data that asensei uses to set your personalised targets and predictions is currently local to the device you performed a workout on. What this means is that you will get less accurate predictions and goals if you workout on multiple iOS devices since only the workouts you performed on your current device will be used in goal setting.
Note, if you logout of a device and then log back in again then you will also lose the local copy of that data, it is wiped when you signout, for privacy reasons.
After a logout or a change of device asensei will learn your rowing behaviour again quite quickly, normally within a couple of workouts. But what it won't currently do is to be able to use results from a specific baseline test or workout to predict your performance in a race, it will use a less accurate extrapolation.