Metamask is also open source wallet but it doesn't come in the form of an application but in an extension form that supports limited networks compared to other service wallets but its still one of the best for token storage but only due to the limited network and not having dedicated app even after all these year is a negative in my opinion.
Imo, that's not the biggest issue with Metamask. It is the fact that there's almost no privacy when using metamask because I remember sometime this year when they put out a public announcement that they have to openly track user footprint using their RPC from sister company — Infura. That, and also the fact that metamask currently have one of the worse UX despite being the most popular EVM wallet available today. I was a fan but Rabby wallet won be over. With Rabby, Users can also see decoded output of the hex value/hash being signed.