Over the past week I converted hundreds and hundred of songs from the old FairPlay format to MP3 so I could play them on my Sonos system. Ondesoft iTunes Converter converted them all and it did it very quickly and without any problems. It even handled audiobooks that were over 2 hours long.
Although it gives full access to every obscure audio options, the interface is really well done; without much thinking I was able to simply select "medium, MP3" for my music and "low, MP3" for my audiobooks, comedy, and other spoken materials. It uses iTunes playlists to organize the tracks, so it was easy and obvious how to select what was going to be converted.
$40 was a fair price for me, considering how easy it was to do the conversions, and how the software had NO PROBLEMs at all. There's even some documentation to get you started.
It's fast. It's flexible. And it doesn't phone home or do any network chatter at all. Because they use avangate as their software store, VISA fraud protection called me to make sure I had actually authorized the charge. (I'm in the USA and avangate is a European company -- it's highly rated by the BBB and is equivalent to Kagi or Digital River), No big deal.
I have no relation to the developer. I paid my money and got a good product. (I'm running OS X 10.9.5 with iTunes 11.4.)