Forge World has finally put these guys up in the store:
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There are two versions, one with plasma pistols and one with Volkite Serpentas.
The plasma pistol guy will be pretty deadly, even to Terminator squads. But it will be also quite risky. With a BS of 5 they only miss on a 1 but a 1 will result in an armour save for them with a weapon that gets hot. With two plasma pistols and a chain fire attack you may be making two armour saves a turn with this guy. Still, even with two plasma pistols and the jump pack this guy works out to only 145 pts, taking out a terminator squad, even if he dies doing it, would be well worth it.
The Volkite serpenta option is a lot less deadly. With AP 5 the pistol is nowhere near as deadly against marines. With two of them and the chain fire rule the guy could conceivably get 8-10 hits on a unit. Against Space Marines that would probably result in six wounds, with two of those saves failed. That would be an extra two hits on the unit.
Not bad but not great for 125 pts.
Against infantry with worse saves, like guard or cultists it would be amazing.
Against a T3 Sv 5+ squad you would be looking at the same number of hits but then you would be wounding on 2+ instead of 3+ and no saves. Then the extra hits would also wound on 2+ with no saves and there would be more of them. On average this guy would probably take out an entire 10 man human squad in a turn of shooting.
Plus they are really cool looking models.