A Hiscox case will fit harder-to-fit horns like a transitional Conn with split bell keys and a larger than normal bell. It will also fit a 10M or similar horn with opposite side bell keys. The only common vintage horns that I have found that will NOT fit in a Hiscox are Buescher 400’s because the bell comes out farther from the body than other saxophones. If you have a Buescher 400, pretty much your only option seems to be the Pro-tec XL alto or tenor case.
The reasons to buy a Hiscox are that it is the strongest case on the market, as well as the best insulated against temperature changes, and also the lightest for travel or shipping. But honestly, I wish Hiscox would add much better internal foam for protecting the instrument from drops and in shipping. The super-hard internal foam can actually damage the saxophone in shipping or if you drop the case, so I recommend that you at least add some softer foam around your sax inside a Hiscox. Or look at the BAM cases, as the Softpack and Trekking also fit many vintage horns, but have softer internal foam.
These Pro II cases are black with blue interior, or add $50 for an ivory-colored case.