TL;DR: so SFX is only good if you want to exchange into Vidanta, and not good for much else, correct?
I remember responding to SFX ads advertising special offers for deposits, and I was ready to give them a prime Marriott, Vistana, or Hyatt week and pay for their Diamond membership, if they could give me a Grand Luxxe week either during Christmas / New Year's or during a two-week March spring break. They did not have that, so I did not go forward with them. I did not want to deposit a week and then wait and hope that it maybe matches sometime in the future.