It works for me too, Paul! It can be a good learning resource, but you have to treat it a bit like Wikipedia - descriptions are written by individuals who may or may not be experts. I bought a lens from one buyer that came minus the rear cell. He said he wasn't to know it was incomplete - he was no expert. Because I treat Ebay like an auction - it is described as such - I work on the principle of caveat emptor/buyer beware, so I didn't whine or complain - I bought it sight unseen and the risk was mine. A lot of people seem to treat online auctions like shops. I don't. I don't expect to be able to complain to the seller before the auction ends, or even afterwards. I should have thought beyond his description saying that he was selling-off all his late fathers gear, that the father was a pro and that as far as he knew everything worked. I should have asked for a picture of the back of the lens. I didn't do any of these things, so I had to bite the bullet.
I wouldn't have the impudence to email someone over their grammar and price - what does it matter? - but I might ask a question to clarify something. Especially since buying that lens! I know I'm not getting a guarantee (at least, none is offered for the sort of stuff I buy) and if I don't like the starting price I don't have to bid.
A little research helps a lot. The holders in question crop up far less often than other holders, and I've even seen decades old 10x8 film holders go for 80 - 100 US, so I'd expect the antique ones to be more expensive. Also, these old holders seem to have been made in a bespoke way to fit individual cameras. I don't think you could reasonably expect to use one as-is with a modern camera. The size and thickness would be different from a more modern film-holder, and the viewing screen would be in the wrong place, so you would most likely have to have a bespoke back made for your camera, complete with viewing attachment. That would bump-up the price considerably! I've seen prices from 300 - 375 US. Just for the back-adaptor. And you have to send your camera (or at least the back part) to the maker so that he can ensure a fit.
Of course, you could make your own back adaptor. If you can do this, you might as well have a go at making the plate holders as well. But if you are going to baulk at a few hundred dollars, you might as well adapt one of your existing film holders to do the job. Then you have to get used to the price of collodion, ether, silver nitrate and salting chemicals. The holders are the least part of it, to my mind!
Regards,
Neil.