OOPS, I should have included "Sram" in the title

I know that the Microshift Advent 9 speed shifters and rear derailleurs are marketed as being incompatible with Shimano stuff, but they don't mention Sram. I have a couple of questions from actual users and/or mechanics. I'm talking about the Advent 9 speed drop bar 1X9 group.

Brief background. Considering this group for an inexpensive gravel bike to leave somewhere so I don't have to schlep the "good" bike back and forth so much when I travel. Thinking about replacing parts if/when I have something break when there might not be Microshift stuff readily available either locally or quickly online.

It's a little confusing: I'm assuming that the Advent 1X9 shifter and RD are compatible with any 9 speed Shimano/Sram-compatible cassette. For instance, I can use a Shimano-Sram-Sunrace with a similar range if I couldn't find an actual Advent? From what I've seen, this wouldn't necessarily be a cost-saving thing, just availability.

As for the shifting: Has anyone actually tried and succeeded or have any words of wisdom on the actual compatibility:

(1) Using the 9 speed Advent drop bar shifter with a Shimano MTB RD? Sram MTB RD? If so, what "speed" of Shimano or Sram RD?

or the opposite:

(2) Using a Shimano 9 speed STI shifter of any kind with the Advent 9 speed RD? (doesn't apply to any Sram *****r since they have never made a 9 speed drop bar shifter).

I'm mostly just curious. We've seen, especially with the old Sheldon Brown wealth of knowledge, that incompatibilities can be overcome, sometimes very easily, sometimes with creativity. JTek, etc. is an example of how to improve compatibility with engineering but sometimes stuff like cable routing etc. can work it out.

Maybe this will be a new area of kludging and innovation since Microshift Advent stuff (9 and X) seem to be well received and increasing market share, but have abandoned the previous full Shimano compatibility.

Thanks.