Only ctrl bar and gloomy sunday are truly worth it. The demonic cylinders are an acceptable choice, if you're one of the few who have wasted enough AP on alchemy to actually be able to equip them.
Demonic Bow: there's r1 pre-reforged HLB, and if you're gonna reforge a bow from r3 to r1 it better be a Bhafel or you're just wasting your money.
Demonic Knuckles: there's r1 pre-reforged champs, and Speedy Crocodile Demonic Knuckle is like 40k repair a point. If you're obnoxiously rich I guess these are passable.
Demonic Lance: read
this thread on why it sucks so much.
Demonic 2h: an r1 HLC or any D-Fang is better. This weapon is just useless trash.
Demonic Staff: Hermit Staff is better, so this is also useless trash.
Demonic 1h: beams, elsinore, bastard ego, who dual-wields nowadays anyhow?
Demonic shield: avon is better since it provides charge bonus, vales is better because it trolls even dragons, guard cylinder is better because of alch hybridness... this is useless too.
Demonic weapons are so disappointing.