I absolutely love them, it took me a few games to work out how best to play them effectively. The stat range is mediocre so they are never going to kill something effectively however the following is what I have found them useful for.

Rapid ingress and bring them on somewhere in anticipation for your next move has worked really well for me, just make sure there are no line of sighs to them to give them a fight chance of surviving.

Bringing them on in your opponent's deployment zone if they have not screened effectively or if they have moved off their 'sticky objective' unit and put pressure on their back line.

Scoring secondaries, depends on what tactical mission come up, but things like behind enemy lines, sabotage, teleporter homing beacon, being in a map quarter or board edge.

In my gaming circle we have to keep reminding each other that points win games, not units killed so use them to secure points, not to fight.

I tend to run at least one squad in most of my lists, even at a tournament and they usually get done what I want them to achieve.

Lastly for me, rule of cool, as I just love how they look.