Just saw the Parking Lot AM transmitter, and I'd be glad to have something more pro than what most kits have offered.
It's sad in this high tech world that any FM or Am part 15 transmitter under $100 is pretty much a toy, or a cheap kit.
Companies must use a separate "wall wart" supply for their equipment, it may already be approved by an electrical regulator, such as UL, so the company doesn't have to apply for approval on their own internal power supply design.
AM is supposed to have range advantage when following the rules, and I'd guess it's good for voice radio, like the pastor's voice. I don't know about the radial field, the kits don't come with radials, but you could connect to a handy ground like a fence post or faucet, I've heard of people doing that.
Bear