There's an additional fee of $10/month/device.
I was at the VZ store on Friday getting 4G hotspots for two new sales guys ($50/month for 5GB per hotspot), and the lady was trying to get me to switch our 15 existing hotspots (all billing $50/month/hotspot for 5GB) to the shared plan and put the 2 new ones on it as well. She claimed it would save us money, and I kept asking her to explain it again as I didn't think it would. I finally said "so we can go with the regular plan for $50/month/hotspot for 5GB (10GB total and $100/month), or we can go with the 10GB shared plan for the same amount of data and same number of devices, but that's going to be $100 + $20 (10Gb total for $120/month). She just said "yeah you're right" and rang me up.