Antique Shur-stop fire extinguisher kit

This fire grenade kit was found in my grandfathers basement it is a bit rusted but still ledgible and the hinges and lock mechanism still function perfectly...it does have all six original glass fire grenades with the Shur-stop logo on each one.  I have taken this to a few people and I get a range from $150.00 to $600.00 value.  I would just really like to know a more accurate price of what it may be worth and actually get it appraised.  I would also like a little more information about the extinguisher.  If anyone knows a lot about these please email me.  Thank you so much. 

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