Dan,
I tried the Tak .73x QE reducer with my Baby Q and did not achieve satisfactory results with anything bigger than a 1" sensor (ex. ASI183). For 4/3, APS-C, and full frame it was horrendous. Terrible star elongation, and I could never resolve it by back-focus adjustment (shims ad infinitum). Even with 1" sensor, tilt was a problem (QE reducer grub screws?) I could not resolve. Finally sold the reducer and now only use the 1.01x flattener for good results out to full frame DSLR.
I thought about trying the TKA82580 CR 0.73X Reducer (no grub screws, so maybe less tilt problems), but they are hard to find and expensive. For now, when I want wide angle images, I am using the Samyang 135 f/2.
I would recommend mosaics with 1.01x rather than using the 0.73x QE reducer.