LIke you Dave, I have used the Amazing Slowdowner for years and still do to this day. I am using it right now to learn some traditional Italian tunes along with some new Cajun tunes. I always recommend it to new box players on this forum. I swear by it and it is well worth the $50 price. One very important point is that when you purchase the ASD, they send you an unlock program. You must save this to an archive disc so you can reinstall it when you redo your PC or Mac.
I have been test driving an Android app called Audio Speed Changer. It doesn't have as many features as ASD and the sound quality is poor at the slowest speeds, but its free, the user interface is good, and serves the purpose. I run it on a Galaxy Note 2 and, so far, find it adequate for my needs until I get back to my PC and ASD.