Idrians casterkill potential on Sev0+HR list

It can happen but doesn't seem reliable.

A single shield guard will make a lot of difference.

Also bringing back attachment to get prey off on caster, and trying to get everything within HR's control, LOS issues e.g. just seems too fiddly to be reliable. It's a good option to have, but wouldn't build a list around it.

On top of the rest of the points, Prey resumes on the initial target if it is still alive when the attachment is revived. So you'd have to kill the other prey target before the Idrians go and if dice or positioning or whatever portion of Murphy's Law may happen, it's also hosed. Or a good focus camp would have the CRA shots at dice -4 on most of the casters that play more forward, so if everything else aligned, you'd have to make sure the enemy caster has 2 or less focus to get the best chance at it. 

Might be better off with 2 man shots, they'll be RAT 8 with Hand of Fate, which is respectable, and POW 14. If the old adage of boosted 12's kill casters rings true, then 6 unboosted, HoF 14's would do fine.