These beings are not servitors, they are thralls. Bonded to the machine with a reward of neural anaesthesia for the successful fulfilment of mission objectives, I personally pity the poor souls who were converted. But on the battle field, these guys are swift, deadly and make me want to invest in at least three vindicators. Just in case.
With T=5 and W=3, coupled with jump infantry rules, these guys are absolutely deadly. I'm a little torn on whether the standard lightning claws are better or worse than twin power fists. On the one hand, lightning claws are (probably) going to be better against space marine legion armies due to the increased wounds they will put out. On the other hand, the increased strength that power fists bring mean that they Ursarax can be more of a threat to other units. Either way: they're deadly.
Their ranged weapon is only a 10" range. But given that these thralls are jump infantry, the controlling player should at least be able to get off one shot before a combat. Within combat, they are a different thing entirely. They can get a blast attack at S6 and AP2 that gives instant death. Realistically, this is nothing that a pair of power fists could not (in most situations) also bring to bear. But its certainly a back up for the lightning claws armed thralls should they need an instant death option against a tough opponent.
They have great durability with T=5 and W=3 each. But they really need to look out for vindicator blasts, as well as D-class weapons that will surely hunt them down with priority.
3 Ursarax, each with two powerfists (185 points)
Something of a baseline build but able to take on both infantry and vehicles thanks to the power fists.
9 Ursarax, 3 with two powerfists and the rest with two lightning claws (455 points)
A full unit with hidden powerfists. This can take on many things in the game (and will make a paste out of legion warriors in all likelihood), but really needs to look out for vindicators early on.