The reflex save on these things is 17, just so you guys know. I've had 4 used on me, never once took any damage. It's no more dangerous than the Hold Person essence or Fear essence that we have had for a while now without any large abuse.
Hold person essence has 14 or 15 dc.
Phantasmal killer has like 15 or 16 (but gives two saves, also since it is instakill you will just get to 0, or be damaged for 3d6)
Sadly for a ranger a reflex save of 17 is not that easy to achieve. The max i can obtain is 13(currently). And i have quite decent dex. (this 13 includes two items that both give +2 reflex, having my cats grace its max 5 bonus and using a universal save +1 item, i have luck of heroes but not lightning reflexes yet.) And you should not forget, that non rogues and non monks, still get damaged by the spell, and it is effectively still 7.5d6 damage. Which on a single item is still quite a good damage output.
Also actually whereas it is quite abuseable in PVP, its true and horrendous power comes out in dungeon farming.
Just to give you an example, with a high ac guy, and someone stocked up with these candles you can easily farm dungeons not meant for your level.
AC guy blocks the door, whereas due to the listen script every moving enemy will come at you folks, and when in mass, you just use up your candles.
5 or 7 such candles can clear out whole dungeons. And i did not even put real thought how this item can be elsewise used or abused.
Sullen woods is a great example, but i can think on at last two other dungeons, which are a lot more rewarding considering loot and xp wise, for a very very long time.
(also undeads have low reflex saves.)
Basicly i could just stock up on these candles, and use them instead of meleeing since, i deal more damage this way, than...i will ever be with my ranger.
(level 20 ranger has 9 attacks, usually having d8/d8 or d10/d6 damage +str bonus, +varnish+enchantment. You can usually get half of these attacks sitting. Which is around half of the damage this candle is able to make!)