Well the idea is to stack as many as possible in your hand until you really need them (or until you can win by playing them -- talking about the upcoming series in general here). So using up to 3 of them shouldn't be cost-efficient, more like a desperate move. From 4 on, they become devastating because of the Chain mechanism.
If you play all 6 at once (costs nearly full fire quanta unupped), you deal 63 damage to every enemy creature, pretty much turning everything to fine dust, including Gravity-pulled defenders, Phoenixes, weak Chimeras, Shard Golems (if they're not immortal)...