The major differences are lower pay for the same job, no protections against unwanted OT, and the certainty of working the weekends since UPS will be a 7 day operation after peak this year. And, of course, it's a combo job -- which means inside work as well as driving, but most people here expect 22.4s will be driving almost exclusively, e.g., the position is part of a longer-term strategy to undermine the pay of RPCDs.
Tues-Sat doesn't necessarily mean they're ushering her into 22.4. Most of the newer RPCDs in my center are Tues-Sat.