I got a Chieftec BT-06B and modded it fairly heavily for mine: Modding the Chieftec BT-06B for Framework Desktop
Highlights:
As far as experiences, the Framework schematics helped me get most of the modding done before the motherboard arrived to a sufficient degree of accuracy. The only issues I have had with the machine have really been related to the motherboard itself, the dumb PCIe slot not being open-ended limiting options heavily - ended up using oculink + external PCIe dock to get a bit more flexibility, the BIOS being the worst BIOS I’ve seen in my life, much more limited than what a sub-10W chinese stick PC ships, etc.