Extron VSC 500 is great but I’d suggest looking out for an Extron VSC 700 as it has a genlock in/out and can solve most syncing issues. I haven’t actually tried this with a Vidiot but you can adjust the genlock signal on the Extron VSC 700 if it doesn’t like it. They run a little bit more but considering they’d also allow for full YRGB composite outputs from your computer instead of just Luma, it’s pretty worthwhile.
If you’re trying to transcode 480i instead of upscale directly from LZX composite out to a HDMI output, the Retrotink 2x or equivalent worked well for me. I run this into a BMI Shuttle Thunderbolt and it looks pretty decent.