I honestly don't think it's worth it. Buying an energy pack would probably net you more.
At best you'll average 4-5Min a run at the lower end of dungeons accounting for killing/entering/exiting. This nets you a result of around 10-12 runs depending if you want to take care of loot drops.
The 50% only applies to monsters killed(which is sort of moot since you don't kill bosses/clear missions when farming).
Because it's a 50% boost, you get about a free run of exp every 2nd run. If you can only manage 10-12 runs a hour, you only get about 5-6 free runs of exp.
I haven't seen the clear times at the higher end of the spectrum, but I assume it takes longer.
Isn't the 100 Fp pack the same price as this or something?

