Hi, Dan, that is not a Heyde figure, it's a homecast, cast using molds made by the Leipzig firm of Schneider Bros. The molds were made from the 1890s up through the end of WWII, and they were reproduced by a couple of craftsmen after the war. I have some original molds in brass, and some repros in a zinc alloy.
The molds were sold to hobbyists to cast their own figures. Some people cast the figures and then sold them under their own labels, especially here in the States, in the Thirties. I don't think Heyde ever used the Schneider molds, though. I don't think they had any kind of flat or semi-round figures in their catalog, though I'd have to check about that.
Your figure could date anywhere from around 1900 to the present. It depicts a British cavalry trooper. I hope you didn't pay too much for it, because it's extremely difficult to date homecasts, and frequently the castings are of poor quality and made of very soft alloys, and if painted, they're often painted very badly.
Hope that helps, prosit!
Brad