Funny, I've never had a problem with the pigments settling down to the bottom of the bottle like some other paints. A couple of shakes has usually been enough.
I've been using Xtracrylics for a few years and like them. Good color range, they adhere well and dry quickly.
From my experience, the way they're advertised as gloss and decal-ready is a bit misleading, as they require quite a coverage to get really glossy, though this is partly connected to my habit of using distilled water, either on it's own or with the brand thinner, for thinning, as I find the paints tend to clog up my airbrush pretty fast if using just their own thinner.
Thinning with only water also makes the paint dry flat (if not built up to heavy coats), quite convenient when painting cockpits or other parts of models that don't have decals attached to them. I usually don't bother fiddling with both water and brand thinner, thinning with just water. Applying a gloss coat or two afterwards isn't such big a chore to me.
Although a bit thin for hand-brushing, they go on well that way too. Just take your time and brush on several coats, letting the paint dry completely between coats reduces the risk of getting brush marks.