Roam takes a while to startup. Once up, it's quite fast to switch between pages. A bit like an IDE. It's still browser based I think, and there are no native apps for Android and iOS. So I feel constrained when I'm not at the desktop.
Notion mobile apps are quite good, so I never have to tell myself I'll do something when I go to my desktop.
Roam as in the one linked below?
Seems like a very different app to Notion.
It solves the same problems for me. Because Roam is almost like a markup language, you can make it do a lot of what Notion does. Especially if you use Notion purely as a personal wiki + task manager.
Notion is much better for businesses IMO. Like I said above, I use it for my startup. Specifically for task management, and even for our public docs site, ex: https://docs.haekka.com/
But, everything is slow these days. Aside from Roam, HN and maybe a handful of native iOS apps, I can't really name any app/site that I use on daily basis that isn't painfully slow.