Imagine a block size war wherein the Umbrel devs are big blockers.

Removing power from the user the way Umbrel does is a problem. Minibolt tutorials are the better solution.

Don't know much about simplex, but it doesn't look much different from telegram in terms of architecture, being open source, and being corporate funded. Its always better to run your own server, but having said that, doesn't look terrible so long as you understand it belongs in the same bar of limited freedom as telegram (feel free to correct me like I said I only took a quick look)