It's a cool (chromium-based) browser with many cool features (they even offer a mastodon instance) that one can as easily decide to use or not use. And the company (from Norway) is owned by the devs themselves not by some huge corp or a venture capital fund ;)
The Mastodon post currently has 277 favourites and 228 boosts, against 66 likes and 23 reposts/quotes on Bluesky. So it would seem their niche fits the Fediverse nicely. :)
Tuta is way overpriced. Stalwart is an All-in-One Mail Server (IMAP, JMAP, POP3, SMTP) that is open source. If Tuta wants my business then sell the hosting/deployment but make the backend open source.