Though the prebooked FP all had to be at least 1 hour apart.
(except that in FP's later days it was sometimes possible to modify them.)
The original version of G+ was terrible.
Then again, FP+ was also originally only 3 per day total. The 4th was added later. The early days of FP+ were a mess. The 3 FP+ either had to be booked in advance, or booked via in-park kiosk, and the wait for the in-park kiosk was crazy.
Even for quite a while after they allowed the 4th FP+, most guests had to add it via kiosk, and the kiosk lines were crazy long.
I remember being at MK, and the afternoon kiosk line was 30minutes. So people waited 30minutes to get a 9pm FP+ for a ride. At 9pm, they would then discover the ride was walk-on, so waiting to get a FP+ actually COST them time.
A small plus of G+ is the ability to book more than one ride per hour.