I've been running a Hewlett-Packard HP t620 Quad Core TC for a couple of years now in that role, with the AMD GX-415GA SOC in it. It's the bigger brother of that found in the APU systems.
The stock configuration usually has 4GB of RAM in them, with a single re(4) 1GBps NIC, and a 16GB mSATA SSD. I haven't had any issues out of mine, which I got for I believe $50 on eBay. They seem to be fairly easy to acquire. Another $25 for a power brick (which amazingly has had no issues either), and you're good to go. These boxes have eDPI display outputs, and optionally have either an RS-232 serial port or VGA output, along with USB 2 and USB 3. They come with an embedded version Windows 10, but I've had no issues running OpenBSD 6.8-7.0 on it, 9front, or LInux. IIRC, it supports EFI booting, but I've only used legacy BIOS boot. If you get one from eBay, I would recommend opening it and verifying that all the internal screws are tight. I had some loose either from shipping or carelessness on the mSATA hold-down and a few other places. Good luck.
