I see a lot of lists these days that are spamming purifiers. Sure you need to pay the Purifier tax of Crowe for 150 points and an HQ slot to make the troops, but they do not make for a well balanced force.
I am really starting to like them myself. They remind me of the old Grey Knights. They both have 2 attacks, power weapons, and most importantly fearless. I hate making morale rolls and this is one of the few units that can avoid them. What you do lose is 1 point of WS, and strength 6 and shrouding. Here is another difference: I had to pay 250 points for 7 Grey Knights with 2 Pscannons and 10 Purifiers with 2 psycannons are 260 points.
But everything in moderation. I will take one 10-man unit of purifiers so my Grand Master can make them troops in objective based missions, but that will be it. They are good, but not what you want to build your army around.