Short answer: they solve different problems. Pickleheads helps players discover and RSVP to sessions. Pickle IQ runs the session on the day — balanced games, waiting list, live Player View, round robins.
If you're a player looking for a game , Pickleheads. If you're the organizer running the session , Pickle IQ. Most organizers we talk to happily use both.
Pickleheads is a great front door: post the event, get RSVPs, help new players find you. Pickle IQ is the operating room: once those players show up, generate balanced games, keep the queue fair, and show every player the live schedule on their phone. Use both, in that order.