They give you greater or equal the number of equivalent runes through card packs.
As long as you have a decent enough buffer of crystals for inevitable new planeswalkers, you should be fine.
It is still worth it to go for 2-6 but 7-16 is kinda meh, esp during double crystal quick battles.
I would always take 5 pack over 30 crystals, when it's a normal 5 pack.
To me it looks like the quick battle reward packs have lower rates then the ones you bought with crystals. If this turns out to be true then crystal are more interesting - at least for me.
A fatpack is something else of cause. Even a bad fp is better then 30/60 crystals.