The whole point of self texting is that its easy, quick and just works. If I don't have an apple product, I already can't access this app. Cool idea but not very useful when the labor is there.
Texting yourself is an imperfect solution to the problem. Note taking apps like obsidian also have "labor" in that you have to pick a location for your note, maybe navigate a folder structure etc. This is a "stream" of notes which is closer to how some of us work. I sort of want my reminders to disappear upwards into the past and not clog my interface, but still be searchable.
I use Obsidian, OneNote for note taking and I can easily create a note just for taking quick notes when using my phone but I still self text on multiple messaging apps because those are something I already use, they are quick and simple.
Having yet another note taking app just puts my reliance on that app and keeps it for a purpose, it also becomes a barrier of sorts for me to enter quick text, that I now need to do it on separate new app/platform.