I second Jeff's post. That's an expensive NEMA plug!
All 3 (install, 14-30, and L6-30) versions come with a 25-foot EV cord, but the 2 with plugs on the input end have a short rubber cord to reach the socket. The install version comes with a longer input cord which may be nice, or it may take more room in a backpack, and the cord on the install version is a more industrial type that looks like it is meant to be stapled to a wall.
I'm wondering if the short rubber cord on the plugged versions wouldn't be nicer to stuff into a backpack and to handle on a day to day basis. On the other hand, the short cord on the PCS-15 that we got with the bike has made me want to get an extender cord to relieve the strain on the cord when I plug it into a socket that is higher than a couple of feet from the ground. And, for $50?
With respect to socket compatibility, if they didn't attach the 4th blade of their 14-30 plug to anything (the install version only has 3 wires and the L6-30 plug only has 3 blades), then you could probably remove the unused 4th blade of their 14-30 version and use it universally on 14-30 and 14-50 sockets.
I wonder why nobody makes a 14-30+50 plug that has a short un-angled 4th blade that would help seat it in either a 14-30 or a 14-50 socket better, but fit into the common vertical space that both sockets have? The standard 110 sockets that can supply higher current than the standard 15A have a design such that lower amperage plugs can fit into the higher amperage sockets, but with 14-30/50 they designed the 30 plug to not fit into a 50 socket...?