I am looking for a 300 mm lens and have come across this one locally but don't really know how well they are regarded or for which photo applications they are best used for

it is a Congo 300mm f6.3 in a copal 3 shutter

how well regarded is this lens and what would be a fair price for it

I should add that I plan to use it for 4x5 shooting not 8x10

thanks for your help