I havent seen that particular advertisement in cosmopolitan but yes its is pretty normal for such positions to be limited to 1. I havent flown privately but i was interviewed years ago for one such company based in Saudi Arabia. Usually most very big companies based in the middle east do have their own private aircrafts - maybe 3 or more - for which they hire cabin crew for. These crews are usually hired for jus one particular aircraft and go where the aircraft to whom it has been assigned for goes for eg one aircraft could jus be for the chairman of the company. Since private flying is a lot more flexible and with higher remuneration a lot of these crews usually dont leave for years and when one does the position comes up. As far as i know in Saudi Arabia they do prefer applicants to be either of European or American passports since visas for most countries are not a problem for them. this being so since you are not listed as a crew on a general declaration form but just an employee of the company. The working conditions are usually fabulous with not a lot of flying but good pay packets and travels to a lot of exotic destinations. If you do get a chance .......go for it.