I agree w/rizq; I don't have personal experience with buying from TSC, but I do have a close friend who bought a couple chicks from TSC last year, just for her layer pen. I'm not sure if the 2nd survived, but the first, a RIR, lived to egg-lay age, and then died shortly thereafter. Again, not saying it's anything that was TSC's fault, just that's the only experience I personally know of.
Anything with chickens invovles a risk factor; if you buy from a hatchery and make sure to go with a reputable one, my personal opinion is that you do get very healthy chicks. However, the sacrifice is they will not be show quality, and may not even be exactly what they are advertised to be (case in point, almost ALL "Ameraucanas" from hatcheries are actually EEs). If what you're looking for are some healthy birds, go with hatchery stock. If you want to show them, or be able to eventually breed them and sell hatching eggs, best to buy from a breeder. Just my two cents.