Just curious, what is the guarantee that all these sites are actually sending notifications for real openings? I mean they are just sending a notification that there is an opening, but when you get there it isn't available, so you think someone else booked it. What if it was not there to begin with? What if the notifications are somewhat random to increase their membership, some are real and people can take advantage, some are not real at all?
How many people have signed up for these services and paid their money, feel satisfied with notifications, but never actually secured a reservation?