I've always preferred the softer rounder lines of the Full Demo Minimalistica, much closer to the beautiful fluid design(s) of the CAISO King Size; the Regular Bulkfiller seems a little more staid, severe, ... engineered .
I had the Regular and sold it when Conid finally decided to produce the Full Demo Minimalistica.
Both write beautifully . It took me a day or two to adjust to the non section of the Minimalistica, noticeably thicker than the concave section on the Bulkifller.
"... the cap of the Minimilastica can be a bit of a hassle, while the threaded cap of the Bulkfiller is perfection."
My experience is the opposite. I like the push cap on the Minimalistica and the Regular seemed to be a little less than perfect when the barrel unscrewed itself from the cap while clipped into my jacket pocket.