1: Never heard of anyone having a metal detector used on them for a drug screen.
2:Pretty much all synthetic urine is safe to use.I like the liquid better than powder because you don't have to mix it up.
3:Can't answer have never had to use one. The only ones that need the whizzinator are people under court supervision for drug screens. Otherwise they are never observed during the UA.

You maybe clean in the time you have. I would pickup some cheap test strips from fleabay and test yourself a few days before your test. If your not clean go with the synthetic.
If you do get clean naturally still folow the dillution sticky. Its always better to be safe than sorry.