Tip: if you already have Raspberry Pi, your can skip purchasing CH347.

RPi has SPI pins and is supported by flashrom.

Original author here. I have a Raspberry Pi, but I still recommend the CH347 instead of the Pi since it's $5 on AliExpress and you can buy it at the same time as the pogo pins probe, which you need. The advantage of the CH347 is that you don't need to fiddle around with the pinout and risk frying the chip if you screw up. You can just plug the probe in (via the level shifter) and you are good to go.

Also, if you are doing the Raspberry Pi, you'd still need the level shifter since the Pi is a 3.3 V device.