Gotta see the exact +item gain. Maybe it really makes a huge difference. It does turn (almost) any familiar into a semi-fairy.
The M-X firework damage is kinda low, but it works for weaker classes in lower levels (i.e. before the ability to 1-hit-kill.) It's certainly an asset for combo-using DBs.
The other pre-combat firework effects... didn't see any in almost 100 advs.
The roman candle skill is a bit pricy for the damage it does (I was using it with a 30lbs Lep and I'm level 20 DB) but, again, must check what variables are at play there. Again, useful for the lower, elemental alligned quests.
Along with the stat gain ability, it will sure help out in ronin.
There's been a while since we've had a familiar equip iotm. As such, it is good. As a general iotm... no.