I teach in a Prep School (specialist subject). Before that I was a primary school teacher. I love working in a Prep School but if I am honest my heart is in the state sector as I felt I could make more of a difference to children. Having taught just my subject for the last 5 years I am sometimes abit bored but now I am in a position where I can start to expand my role more.
A Prep School is really driven by the Headteacher and they can make a huge difference to the ethos of the school. Check out if it is a private business or charity. If a private business a school can literally shut down over night. This has happened to a few schools in this area recently.
PROS:
less stressed, trusted to get on and teach- there aren't endless observations, I can decide exactly what I want to teach and can be more flexible with planning, classes are small, no major behaviour problems, inspections are by IAPS who seem much more constructive and less destructive than Ofsted, resources can be easily ordered if needed, children are allowed to be children and have fun and fresh air!
CONS:
can be lonely, sometimes need to battle with other departments for time to do things, parents are more demanding- some act as if they own you- they pay for a service and expect their money's worth (but can also be VERY supportive), days can be longer (eg children arrive at 8am, you could be working until 7pm if doing a club), Heads don't always recognise Unions and can sack people easily!
I would say go for it and see what happens. It doesn't have to be forever if not for you.