Going rate is around $600, so if you are looking at $900 I would pass on it at that price.
For that money you could get a Benelli M-1 or M-2 or maybe even find an M-4 any of which would be an Uber-Auto Combat Gun.
As a collectable / costume gun - The HS-10 rocks!
As a actual fighting shotgun - the HS-10 sucks!
High Standard is LONG out of business and getting the parts (shotgun not pistol) even from the folks who find the hard to get stuff like Gun Parts or SARCO is tough. Figure the parts will break, and then you are looking for something either not available or very expensive,
I have owned both 10-As & 10-Bs and neither was dependable enough to be more than a range toy. You WILL get a lot of comments though!
B.T.W. - I always wanted one after seeing "Thief" (the Mafia Hit Guy - (played by ex Chicago Cop Dennis Ferrina) used a High Standard 10 when getting nasty!)
BIGGER_HAMMER