This! It's almost like a safer ICO -- following the line of thougth that ICOs are ways for non accredited common people to get in on something with big potential upside - but unsafe because of the large pump and dump and scam potential - whereas here you know that S+C & Palihipitiya are for real.
To get in only paying 7% (i.e. at the IPO), you have to already be a wealthy investor so you can get some of the IPO stock.
The 18% difference is your fee for deal access basically.
I'm not saying it's right, but it explains why it makes sense.