I've been using posthaven for 4 months now, and this is what I think about it.
First of all, it's a paid service. 5$ per month, but I believe that is what allows it to be independent and sustainable. It doesn't ship new features, but it's a feature itself - we all know what happened to Evernote.
I like the simple editor, without blocks bullshit like in the Wordpress, and generated HTML is not a freaking mess. What drives me nut is that some images (webp only probably?) are not visible after publishing. BTW, the media itself is available, it's uploaded successfully to posthaven, so the problem with the client code. (More precisely, the problem with the .posthaven-post-body .posthaven-gallery .posthaven-gallery-loading img class, which hides an image).
They say that this service is designed to outlive us. I don't believe in that. I don't believe that posthaven will outlive its founders, that's just a fairytale.
I also like the "Read only mode" feature. This is when you pay for 12 months, and then if you stop paying, your blog remains available for read only.
The "Post by email" feature is also great - you can publish a post with just emailing to a specific address. I've tested it only once, though.
The themes are awful. None of them is near even the "pretty bad" level. You pick a theme not because it's good, but because it suck less than others.
Summary
I like it and plan to keep paying for it. If you want to check for alternatives, you might look at bearblog, https://mataroa.blog/ or exotext.com