A long time ago in SVP 3 I just sent in a donation and I guess the devs kept track of that and sent free licenses for SVP 4. I don't normally support things (it's been like, Wikipedia and this) but I felt like the product was great and worth sending in $20 or whatever it was.
The product does a lot while asking very little from you, and the automatic setup was nice. I had read about avi-synth scripts before but it was a bit difficult to set up so I never got into it; it's nice that the setup takes care of all the steps for you.
But again that's your personal preference; I can't help you from a features standpoint, more just from a "did you feel this software was worth $20" standpoint. I thought it was, and probably more given how much video I watch on my PC.