First, thank you for your work on this app!! It's a real contribution to the tools available to language learners. I've been using it A LOT over the past 5-10 years to improve my Chinese vocabulary and find it very helpful.
Second, a request / suggestion for future development: It would be great to be able to have different types of flags, similar to what's available in Microsoft Outlook. I generally use the flags to mark cards where I've seen an error in the card that needs to be corrected. But I'd also like to flag cards that I have a lot of trouble with (e.g. I keep getting it wrong for months and months every time the interval gets to be longer than a few days) so I can target them specifically. So two (or more) types of flags would be helpful.
Best,
Mark