I have an Oct UY and it works well since we usually go to WDW twice a year, in the months of Oct, Dec, Jan or May. The 100% banking deadline for an Oct UY is Mar 31st, so cancelling a trip scheduled for Oct, Dec or Jan would be no problem, provided we cancelled 31 days or more before check-in. (If you cancel 30 days or less from check-in, your points go into the "holding account" and cannot be banked, and can only be used to book a stay within 60 days of check in.) It also covers us pretty well for our early May trips since we would have to cancel 31 days or more in advance to be able to bank the points. We might still be in late March (in our 100% banking window) or worst case, early April in our 50% banking window. Since we do two trips a year, it's unlikely we would be using more than 50% of our points for that May trip, so we could still bank all the points from a cancelled May reservation.
We never plan to go in June, July or August (too hot) and Sept isn't high on our list either (risk of hurricanes) so an Oct UY works out great!
ETA: Worst case scenario for us would be if we cancelled a May trip within 30 days of check-in. The points would go into holding and would have to be used by the end of our UY (Sep 30th). If that happened, I think I would find a friend or relative who needed a vacation and would put up with the heat and humidity in exchange for a cheap WDW vacation!