I believe the windSUP rig includes a 2-piece mast. The 6-ft long "carrybag" shown in their videos assumes you want to walk around w/ the mast already assembled and dressed w/ the sail. But if you break it down in b/w uses, then it's really just a std 2pc mast, boom, foot, and windSUP sail. All of which is easily stowable inside your car.
In lo-wind boardsailing, the boom is your steering wheel: you grasp it at many different locations along the boom arm, hang from it, underhand it, use 'body english on it, etc. etc. The iRig, you lose that for a few loosey-goosey handholds. (Plus, from the few vids online, it looks pretty underpowered.)
I'd go w/ a windSUP rig. After you learn how to rig/de-rig, it usually takes under 10min to get going.