London “idli dosa batter”?

I am moving to UK from US. I found that I. yo the stores give a pack called “idli dosa batter”? So, not two different batters reflecting the differing proportions or different fermenting times, just one thing.

So first question - how does this work? Do you just use a dosa batter for your idli? How does that turn out? Or, do you use a idli batter for dosa? Or - are you adjusting each time tou buy batter to make it for idli or for dosa? I mean - they are not same batter. Are you just resigned to something half-way acceptable? All I sights welcome!

Second - given this issue of same batter for both, whoch batter do you find reliable and how do you use it?

PS - I can see adjusting a idli batter to make it dosa. But I can’t see the other way around. All tips welcome.