Yes — without the anti-pulsefire effect, the fire burns very fast and consumes the victim entirely, body and soul. Newt's invention will slow this into a more "regular" burn, which, without anyone then figuring out a way to extinguish it, will eventually burn their victim alive anyway, like normal fire would. So if he tests it on himself, he should have someone around who can actually put it out after.

That is fine, as long as people remember that these will obviously not be available until towards the end part of the fight.