This video is an analysis on the rewards cards and potions. Is it worth it to buy potions for your quest and season rewards?
The short answer is not really. Expected value of profits are pretty much the same. If you want to boost your golds or your legendaries then go for it, but the profit opportunity has been pretty much arbitraged away given today's prices.
One thing I did not mention in the video is that this is using the conservative bid value for GFLs rather than the ask values. So you might come to a different conclusion if you think the ask values are more relevant than the bid/DEC values:
It's always a little sad when markets are behaving rationally. I like to be able to take advantage of those arbs!