I have few HMO's and advised by solicitor to grant Assured Tenancy, NOT Assured Shorthold Tenancy. They drew up contract very similar to AST but written at top is This is a Assured Tenancy, and wording within it saying ..this agreement does not in any way form a shorthold agreement'...or words to that effect.
This is good as by law I was told as these agreements are not AST's but Assured Tenancies I can hold their deposits in my own account and not a TPS account. Which for HMO's is great as if tenants vanish in the night I can simply use deposit to cover rent while I re-advertise and find a replacement.
My opinions are exactly what you would expect, my own!