Hi, Em Westlake!
Thank you for your question. The 520-MPU-DST does include the metal pop up, RP26533. If this did not come with the drain assembly, we recommend to check with the store you purchased this from for a return/exchange. If this was an open box item or a clearance item and came 'as-is', you may have to purchase the drain assembly separately. Here is a link to the drain assembly kit:
The difference between the 520-MPU-DST and the 520LF-WFMPU is that the 520-MPU-DST features our Diamond Seal Technology. This includes flexible, PEX supply lines. You can learn more here:
The 520LF-WFMPU is also Lead Free. This includes 3/8" O.D. copper supply tubes. Here is a technical specifications sheet for both units:
Date published: 2018-04-20