Why can you never get my name right?
Mandrakes are an Elite Choice and are rather interesting unit, ordering light on these guys is probably a good idea. I used them before but that may be changing a lot since Incubi are now an Elite choice instead of a HQ Retinue choice.
Ravagers are a Heavy Choice that mounts two more DLs than a Raider does and no troop capacity. With the addition of some of the new Heavy Choices from what it was before, Talos or a Ravager, The ravager might see a lot less play since it still is lightly armored, and it is still not a Tank. So I believe it will be more of a so called 'vanity tank'.
Hellions now this is where it gets tricky. Last codex they were one of the worst units to field, this codex they are a lot better. One special char makes them troops choices if you take him and their ability to yank characters out of combats and drag them off with them has people looking at them in a new light. I think though it will be a small amount of people that will be getting them but thats my opinion, since the bikes or scourge are still better Fast Attack choices than the Hellions. So light ordering is probably for the best.
Now with that all said, I want one box of each for myself anyway since I want to be able to field Old and New of all the models