The feature set as a whole isn’t unique, but the way in which the Lydia app presented those features (and the use of Euro which would have been a selling point for some) were the differentiating factors.
It seemed to me, too, that the premium offering wasn’t available in the U.K. It was supposed to be free if you were under a certain age (I think it may have been 25?) which I was eligible for, so I tried to sign up to it but it never worked? I always got an error and I assumed this was because it wasn’t actually available here and the upgrade page showing was a bug. Looking at the app now, all references to it seem to have been removed so that would maybe prove us right?
I never managed to get a card from them, I think by the time I signed up the option to get a card had moved behind their premium offering, but it sounds like a nice card.
All their functionality can be replaced, I suppose, with a combination of Curve (as you say, and possibly with Curve Send which I haven’t tried yet?), Revolut and a Starling Euro account, but they are a sad loss nonetheless.
There is only one other person in my contact list who has an account so, as you say, it seems they are tiny!
I wonder if they have widespread uptake in their home market of France?