A flight booked through a TA is essentially not different from the same flight booked through an airline. If you are eligible for seat assignments, CZ will do that for you although this might have to be done over the phone (I don't believe you can do it online with them). The main issue with TA bookings is that most won't give you the fare bucket and many CZ fare buckets do NOT earn any miles on FB so if that is a concern (ie if you want miles) you might want to call them or most likely for a cheap fare you will get 0.