If you have a large library of music and/or samples that are missing the key/beat information, this is a great program.
I would agree with the previous posts in that it's good to train your ears first as it will help in the long term with your musical abilities. However, for those of us who have been collecting digital tracks and/or converting vinyl collection for many years and have amassed HUGE track libraries, labeling by ear/piano key can quickly become a pain in the ass when sorting through 6000+ tracks.
Key metadata can also be stored, making it extremely useful for programs like Traktor/Serato. To add, its BPM matching is quite good and you can specify whether to have the BPM in decimals (and by how many places) as well as having the BPM round up to the nearest number...which can be embedded in the metadata (or filename) as well.
I don't use the BPM unless it's for labeling samples that are missing data. However, the key labeling can be a life saver when it counts.
It's a great product worth the cost of admission, and their customer service is fast in getting back to you. For under $100, I'm happy with it.