As someone who’s had a single-user Mastodon instance for two years now: I love it. It’s definitely not for everyone, for reasons mainly stated in the article. However, if you like a more personal, highly-curated federated timeline, a single-user instance is great.
I 90% use Mastodon to keep up with my friends’ posts and see art and animal pictures (and I hate interacting with strangers LOL), so I curate my instance to only subscribe to them. For the remaining 10%, I have a secondary account on a larger instance for when I want to read the news etc. It’s worked well for me, but again, it’s surely not for everyone!
Honest question : Why Mastodon ? I had a single-user instance very soon after discovering the fediverse, but the needed stack to run a Mastodon instance is really insane compared to something like Akkoma / Iceshrimp. I would never use Mastodon for a low number of users, including all the limitations compared to other micro-blogging activitypub compatible services.