It all cuts down to 1 question for each unit :
- Reavers : they are fast, resilient, can hit hard in melee, have access to mortal wounds and blasters. But does it justify their price ? Yes : take them. No : don't take them.
- Hellions : they are fast, can hit hard in melee, have tons of shooting attacks and have hit and run, but they die to any form of shooting. Will you be able to protect them enough to use their offensive abilities ? Yes : take them. No : don't take them.
I played the boardgame once, it was pretty boring. It almost looks like an excuse made up to sell those unwanted Hellions models (they sucked in 7th edition). But yeah, for the price that box is awesome.