All else being equal, 4 different tenants over the course of two years significantly increases your chances of getting a bad one who will over-hold. If you're not up-front at the start about the tenancy being limited to 6 months, the surprise of getting termination notice later might tip an otherwise good tenant over the edge into over-holding.Yes you still run the overholding risk - no more than you do at present - but the tenant has no legal defence.