There's a good bit of history on the EBay ad about the real thing written by an expert that's worth a read. Basically experimental high pressure steam loco designed by Gresley with a boiler that utilised principles from steam ships. Was a top secret project, hence the nickname 'Hush hush'. Was rebuilt later on and ended up looking like an A4. She was scrapped in 1959.
l.H Loveless comission British outline locos made by hand out of brass in South Korea in o gauge and gauge 1. This is gauge 1, 10mm top of the line stuff. Would kill for an O gauge one personally.