It doesn’t work for me. I am still on version 1.7.1 (1.7.1.346-4b08409a to be exact, according to the settings menu of the app; iPhone 8 on 13.4). Neither option worked for me. Choosing “Unlimited currency” and then trying to buy something with gems caused the game to crash. (I also tried using people and XP, just in case those were the currency, but nada.) The “Unlimited cards” option didn’t give me any extra cards, either.
I have the crash logs courtesy of Cr4shed if they would be helpful, but since there’s an update now pending for the app (which I imagine would probably break it anyway), they’re probably of even less use than otherwise.
By the way, I really appreciate all you do for the community! Thank you so much for putting your time and effort into these.