[@Raijinslayer]

What Kal said. It is logical, true demon or not, they will still get affected by the magic.

Devil Slayers are different from DSs:
[u]Nigh[/u] instantaneous element, e.g instant freeze from Gray/Silver then it should mean if there is a fire devil slayer, instantaneous burn like Sasuke's Amaterasu.

Resistant to curses through absorbing them which allows them to demonize themselves, see Gray tanking and absorbing Mard Geer's Memento Mori(a hyped spell that can only kill Zeref). [url=http://ptanime.com/wp-content/uploads/2015/02/Fairy-Tail-411-Gray-e-Natsu-Sobrevivem.jpg]Here[/url]

Their eyes are different color. Which is theorized that it allows them to see weak points/curses. See Devil Slayer Gray vs EF Tempesta. [url=http://fc07.deviantart.net/fs70/i/2014/244/3/7/fairy_tail_manga__gray_demon_slayer_badass__by_diebitch2947-d7xiydq.png]FATALITY[/url]

If the damage is 50 against humans, it does 50 x 2 against demons.

[u]Devil Force[/u] is still a theory but it is likely to happen. Most fans are speculating Gray demonizing himself is considered Devil Force.

That being said we don't know the full extent of Devil Slayers.