I'm in the same boat. I liked it and sang its praises for a while, but eventually ended up reaching for Contacts more often than not. I don't even think I have it installed any more, despite buying it back in the day.
Likewise, I don't "get" Fantastical. I owned and liked Version 1, but was disappointed by both the new look and subscription pricing when it moved to version 2 (then 3), so moved on. I've since found I could get all the same functionality of the old version (which is all I ever wanted) for a one-time $15 fee from Calendar 366, which I now use religiously.
Chatology, also from Flexibits, was a godsend for a while as it provided a band-aid for sudden shortcomings in Messages, but Apple seems to have eliminated the need for it in recent MacOS updates.