You really should download and use the free trial to decide for yourself. In fact, all the slow-downers on the market have free trials.

In Capo, you have all the functionality you need, with the limitation that after 5 minutes of audio pass through for a given song, audio quality will begin to degrade.

Learn a handful of songs with Capo, a handful with the others, and let me know (use the Feedback item in the Help menu) how it went!