I wonder if a personal streak makes much sense though?

I think at that point product-specific streaks are more useful. So you can earn a streak for going to the gym regularly. But of course, having to do so daily would probably be too much for most people.

We could make those product-specific streaks customisable as they are more personal by definition anyway. You could just set your own goal (e.g. every other day). But then it's starting to sound quite convoluted.

Anyway. Adding a way to mark products as personal and not have them count towards the streak might get us most of the way there.