I thought about sending in the rainbird one but as pointed out on the site you linked you are then kind of tied to their products which isn't that big of a deal maybe.

Do they always use PVC for the main runs ? I was expecting it to be some kind of flexible tubing like PEX.

It sounds to me like you go from your main water supply to a valve. Then run the PVC from that around where the sprinkler heads go. Then you tee into the PVC and connect the heads using a possibly flexible tube.