Yes, I do have some experience. The Quail Hill Trailhead does have a open public trailhead that goes along the bottom of the hills. Not much really. Last time I was there (Oct?) it was closed off for maintenance. Kinda surprising since it's only about two years old.
The QH TH is on Shady Canyon just past the first traffic circle west of the 405 on the right side.

From that trailhead, there is alos a public use path - paved - going west up and over (steep) the hill into Turtle Rock that ends at Turtle Rock community park. Don't leave the path in Shady Canyon or the security guards will harrass you. They had to let the public access that path thru the gated community and they don't like it.

As far as some other rides in the QH; they go thru Irvine Company and Irvine City land managed by the IRC. Those rides and hikes are docent led (free = no $) and you must sign up ahead of time. Follow those IRC links to sign up. (Bommer has some open access days where you don't need a docent with you at all times)

They have other areas as well in the greater Irvine area.