A lot of people prototyping in the IoT space are using the precertified modules.
There's not much more to it: the transmitter is already soldered to a small piece of PCB but has the antenna and necessary tuned discretes on there and ready to go. Doesn't add much to the cost: like BillinghamJ says it's the certification time and cost that's not really worth the trouble if you can just amortize it into the cost of the module.
