Lock Boxes for contractors

I just purchased a three flat and am having one of the units remodeled. The contractor said he would like to put a lock box on the door so his guys can get in without him having to be there. Is this normal practice? I just feel that those things are an invitation for break ins. I have other tenants in the building as well and don't want them to feel the home isn't safe.

Any feedback is appreciated. Thanks.