The real problem with Gjalls is that they don't drop anything of good value. The single Bile Bag you get is worth a few bombs (I don't use bombs) and other than that it's only needed for crafting the weak/underpowered Jotun Bane axe.

The Ticks are more valuable than the Gjall cause the Blood Clots are used for some good things. I often get the Gjall low and then just parry its fireballs waiting for it to spawn Ticks a couple times for more Blood Clot farming.