If you purchased RadioCaster less than a year ago (on or after January 01, 2015), then you can get this update for free. We provide 1 year of free updates so that users can get bug fixes.
You have to pay $19.95 only if you purchased RadioCaster more than a year ago, and you are free to use the version you have, it will never expire. I'd like to note that paying for this update gives you another year of updates as well so $19.95 is not only for this version, but for futute updates and bug fixes too.
RadioCaster 2.4 compared to 2.3 has some new features and UI changes (like display name for encoders, individual reconnect timers, ...), but most importantly, there are lots of internal changes making RadioCaster more stable, reliable and faster.