you've gotta think what you want out of it, if you put them on a zero hour contract it will suit you in the bad times, winter etc, but who wants to give long term loyalty to a boss who cant promise regular hours, you risk training up your next opposition then. just a thought 
thats a very good point, something i have thought about, but it does / can depend on who your employing, the guy ive got on this is very happy and always going the extra mile to keep things working, given the work i would have him full time, hes been on this zero contract for around a month but as yet hes had nearly a full weeks worth of work each week, it seems to suit us both, hes not dAft and knows the score, it works well for both of us, (i also have full time staff), it depends on each person / companies position and the person working for them as to if it would work or not,