I took a look at Mash. It's definitely not self-custodial, and I didn't find a browser extension, but I do see that they have partner integrations. It's kind of interesting for what it is, basically a content monetization product built for earning bitcoin. As a standalone service, I might use it, but it's not a suitable wallet replacement for nostr:npub1getal6ykt05fsz5nqu4uld09nfj3y3qxmv8crys4aeut53unfvlqr80nfm.

You get a Lightning address, but there is no compatibiltiy with apps like nostr:npub1xnf02f60r9v0e5kty33a404dm79zr7z2eepyrk5gsq3m7pwvsz2sazlpr5, so you're basically locked into their website. There's also a 100 sat minimum to send, so it's not really useful for zapping. If you use it to earn sats, you'd want to send them off to a different wallet at some point where you can custody them yourself, with Zeus (node in the phone) nostr:npub1mutnyacc9uc4t5mmxvpprwsauj5p2qxq95v4a9j0jxl8wnkfvuyque23vg, or Phoenix.

The tl;dr: It looks fun, but you still need to have other wallets anyway. And definitely don't store all your sats on a custodial service.