I can't comment on the assortment you're considering, but I love Cackle and have had very healthy chicks from them with zero mortality. (and I'm a total chick newbie- I've never brooded chicks before)
Now, I didn't have them shipped... I don't live terribly far away, I wanted a smaller order (and a mix without ordering 5 min of each breed), so I ordered and picked them up myself. It was when the season was winding down, and they were very willing to let me order odd numbers (one of this, one of that, a few of this, etc). I don't think this is something they usually do, and I wouldn't probably even ask in peak shipping season!
Anyway, I ordered 7 pullets, I got eight. I was sure my freebie must be a cockerel (that seems what most freebies will be anyway), but my birds are 16 weeks now, extremely healthy, and ALL appear to be pullets. (unless one of the EE's is really holding off giving ANY clues at this point... I only ordered 3 EE's, got 4, but they all appear to be pullets) The four EE's are beautiful colors, all different, 3 of them with quite a bit of blue in them. Can't comment on egg color laid yet, but I'm thrilled with the variety as they've feathered out.
I think what you may get in your assortment will totally depend on what time in the season you order. For instance, when I ordered, there were only a handful of breeds available...and they were only hatching for a week or two more. If you wait until they have a lot available for many breeds on their site, your chances of getting a nice assortment is going to be better, I'd say.