My take on zigs: I use zigs more and more each year and catch more as a result. Last year there were at least 2 sessions on which I would have blanked if it wasn't for the zigs. I don't always go straight under the surface like most do, in fact I normally start by splitting the depth into thirds and fishing one at the bottom of the middle third and one at the top of the middle third (particularly at night). Only on the brightest days do I pop one under the surface and even then it's only when there's a breeze on the water and I can see carp in the very upper layers. I don't find zigs are the answer when they're milling about on top on the hottest, calmest days.
I use the Fox zig alingers with balck foam which are great over a hatch but have also had success on tiny bright 10 mm over-flavoured pop ups.
I use lead clips with the smallest lead I can get away with. It pays to drop the lead (I'm not a fan of dropping leads but it's necessary with zigs - it's horrible playing them with a lead attached and I've dropped fish because of it).
I avoid the pre-stretched zig lines, they have next to no abrasion resistance so can't deal with the weed in the Nene Valley - I discovered this the hard way. My mate put me onto X Line in 10 lb as a zig line and it's been absolutely brilliant.
As said, the hardest bit about zigs is getting your head round it. I used to try it for an hour here and there but would think I was wasting a rod. It wasn't until I'd caught a few I dared keep them out for longer periods. The trick is to use them for a reason rather than for the sake of it - most guys only whack one out when they're struggling on the deck. I'll put them out where I know there should be carp (e.g. when I can see them from the trees, see a hatch, or can see them topping over bait but can't induce a take). I find chucking a zig at a showing fish is at least as effective as chucking a single (e.g. a pop up) at them, probably more so.
They are very, very effective fished two thirds depth off the deck a meter or two off the entrance to any shallow areas or bays.
Again, I find you need a breeze on the water, regardless of time of day or season, for them to work really effectively. I never put freebies out, just attracts the bird life.
I still struggle to get my head round them a little bit - even if I've caught 4 on zigs and none off the deck I still refuse to put all the rods on zigs, I always need one on the deck. Crazy I know.