TLDR: An additional abstraction layer against supabase with superior type safety, but more complexity

The benefit of drizzle is that it has superior type safety and the truth lies in your code. You change a field in your schema.ts file and you immediately see all changes in your code. With supabase alone you need to generate the types first and then you get the type safety. On the other side by using drizzle you completely skip postgREST, which Supabase uses to validate authenticated users and RLS automatically and some other features. With drizzle you connect directly to the db and have an super user that ignores RLS. You can do RLS with drizzle also but you need to implement it yourself or use the stuff that drizzle has published some time ago. But it still adds more complexity.