As pluses over PMUA's SDC, you can do at 24 hours and can do different routings.

As a minus, you have to have the same fare class as your original ticket (often making SDC difficult-to-impossible on cheaper tickets on many routes) or pay an upfare. The UA rule of only needing H buckets available (even if on an L or K fare) made it easier given H was almost always available.

Overall, the new method is a big plus when it works IMHO due to the wider time window.