IIRC, the docs say you're supposed to be able to use it with a trial account. I think I did try to sign up for the other kind and ran into a wall where I had to contact support or a sales rep, and the last thing I ever want to do is talk to Oracle sales.

I can second this. Back when I first set up my free tier resources there I confirmed this with a sales rep, PAYG accounts will have immediate access to free tier resources, that limitation is only for trial accounts.