I see nothing intrinsically wrong with a short probationary period PROVIDED that it is a two way street so that the teacher may be free to leave during the probationary period should he find the school not up to it's promises in the contract or that he dislikes, with good reason, any aspect such as below standard accommodation, late payment of salary or unsavoury coduct by the management.

No FT worth his salt should be scared of being assessed as long as it is fairly conducted by persons qualified to assess. Assessments early on in a teachers employment at a school are very useful to weed out those making false claims about ability to teach, rather than entertain, in establishments interested in education, not just profit.