I had the older EF version and wasn’t too thrilled with it. Don’t know if the RF version is any better. If the RF is just a re-mounted EF version, then I think there are better options out there.
I tried a friend and it is probably the poorest lens I've ever mounted on my R bodies. I would look at the RF100-400mm which I find is a real nice lens @ it's price point.
One of the first places I look is Ken Rockwell's site. See his review. "It's the old EF 75-300mm f/4~5.6 III repackaged with an RF mount so it can be used on Canon's mirrorless cameras. ... I only suggest this lens for use with stabilized cameras."