Quote Originally Posted by ARMOR View Post
Or am I missing something in that if you use credits it is not guaranteed to work your boosts?
That's correct, iirc the word "chance" is in the mouseover tip. Gems always give the boost, credits only give a chance to boost. Getting the 20% boost costs 20k credits per attempt, or 2 gems. After that, getting the 40% boost costs 40k credits per attempt, or 4 gems, etc.