If I give my RAF files a color-tag in Photo Mechanica (straight from card-reader) and then press control+E to sent it to LR6, in the Libary of LR6 the colored tagged photos are tagged, then hit Import, It takes about 5min to load those tagged photos into LR to edit.
If I do the same with Canon RAW it takes only 20sec.
If I open LR6 and view photos straight from card-reader and the tag them, it takes about 20sec to import.
The main reason I use Photo Mechanics is to view the raw very fast straight from a card reader and tag them. LR is to slow to do this.