Sun Dec 04, 2016 10:13 pm
I'd say go for it, at least getting the bonus offer for 1st purchase is pretty worth it IMO. You should be using gems for heroes gacha if you don't have any decent unit but once you have a decent team, you're gonna need lots of gold to strengthen them. but you might wanna save it until you really start running out of gold. (the promotion last like forever until you buy it.)
For gold mine, Dragoon and Ninja are the best classes hands down. Dragoon can attack a whole row and jumps to ladder if needed, Ninja can refresh everyone's turn with some luck and if you know what to do, you can eliminate all rocks and move on in a single turn. if you don't have any of these, bring your best DPS heroes.
Also once you can manage Heroic map, always go for Legendary gold mine.