I have had them for nearly 20 years for the same reason -- a large gap in between my front teeth. I have had no problems with the veneers at all. No looseness. No discolorations. The color matches my real teeth very well. The dentist showed me the color choices and we talked about it several time before choosing.
My problem is with my real teeth. Over the years, my real teeth have migrated a bit farther apart. I need slightly larger veneers to fill the gap in better. I'm still holding off because they still look way better than when I started.
Feel free to PM if there are any questions you think I can answer.