I don't even think giving them an Eldar Warp Spider pack would be any better venkelos. Eldar tech IIRC tends to be psychoreactive and requires their psychic abilities to even work. Without that they tend to be inert and just a dead weight. Even picking one up and trying to use it they would need silly levels of training and theres no guarantee of it working. It's like trying to use Project Indigo and there's no safeguards in place of it getting you in the right place or even able to rematerialise yourself at the other end and most certainly the mechanicus/inquisition would want that pack if they found out about it.
There are however other things you might want to think of. There is something in BC which might interest called a Displacement Field (I think, name is patchy not got the book). Basically it works as a forcefield and when shot at can move the player 3D10 in a random direction, trying to displace them out of the way of the shot however if there are any trebles then they suffer consequences. What about that as a compromise?