I'm pretty sure that the likes of Hornby, Bachmann, Dapol etc wouldn't even entertain manufacturing a Fell.
A one-off - subject to more than average modifications throughout its life - scrapped long ago - hardly the easiest subject to model.
The larger, and more recent, a class of loco is, the more chance you have of getting pretty much all the minute details correct. Helped immensely if examples of that class are still extant, plus the quantity of digital images you have available at the push of a few buttons on your keyboard.
My comments are this:
Does it look like most buyers' perceptions of what the Fell should look like ?
Is it well made and does it perform well ?
Is it good value ?
Re the price, they cost £150. A small shunter such as a Heljan 07 will cost you a discounted £170 new. New Bachmann class 47's over £200, discounted. So, given you only have the one loco to cover the tooling costs, I think that's pretty good.
It may not be perfect. But given that having a kit built up and decorated would cost you multiples of £150 then for many people this will be perfectly good enough.
And me ? I've got a black one and a green one....