Since the price changes, they have been my cheapest option only once and everything went fine, which is no surprise since it was couriers please.

It says on the label who the courier company is, so if I ever get a label that says fastway, I will cancel it (I'm assuming I can do that).

The option I use that is sometimes the cheapest is transdirect.com.au, same type thing as sendle, except that it offers different prices for different couriers, and who is cheapest depends on destination &/or origin.