Mark
I have not seen one from that die before. There are a considerable more number of striations (lines) on the ribbon ends either side of the Hussars title than the Gaunt badge in Post 1: albeit some of them have been polished off.
The Marsh catalogue badges follow the Gaunt die style where as yours is noticeably different. It's a shame it is not marked but as you suggest could be a contender for a Firmin made badge who were the other major supplier with Gaunt at that time.
It would be interesting to see if any other members have a badge like yours.
A quick look on ebay has a Gaunt marked die cast collar
https://www.ebay.co.uk/itm/224535874...AAAOSwothg8KX3
as well as over twenty die struck fakes from the Marsh die with cap badge sliders. None of the ebay one shave your badge's designs which is a good sign for it.
Alan