I checked out a handful of similar apps and found this one to have the best mix of simplicity, data tracking, customization. I like that a given workout is laid out as one straightforward page, so you don’t have to go in and out of each exercise while you’re logging them. I also like that the your history is readily accessible from within an active workout, which makes progressive overload a lot easier. It’s easy to look at the statistics for a variety of useful factors over different time scales (volume per workout, volume per muscle group or specific exercise, number of reps or sets per X, etc). I could nitpick a few minor things (it’s crashed a couple of times, without losing anything), but it’s a very solid, smartly designed app that I expect to rise in popularity, especially since the developer is responsive to feedback and always improving it.