P300 is it VLAN passthrough?

Yes, that’s correct. It is the functional equivalent of an Ethernet cable (except half-duplex) - whatever goes in one end comes out the other.  Easy to configure and deploy, rock solid reliability, built like a tank. The only negative is that it’s only supports 2 streams. Most competitive products have had 4-stream radios for over a year at the same or lower cost.  Some support 60GHz 802.11ad (gig f/d, 1500 ft max) with 5GHz backup.