now how in the hell would that help matters, autumn? The horse needs to accept a simple, fitted bit first. That bit has a frickin fixed port. It would be WORSE
I've always heard chestnuts have more sensitive skin. They get prone to the summer ickies and are sensitive to metals. And forget about the spot on fly treatments!
anyway, nathe bits are
http://www.bitofbritain.com/Nathe_Loose_Ring_Snaffle_Bit_p/0121.htm
This is the only nathe bit I know of. The dog bone shape and it's a kind of gum rubber.

Average, for horses with some experience at this level