Consider it a blend of good design, compactness, looks - and rarity. These can be made into really pretty rifles, are very strong by design and - if you omit the safety features - have relatively few parts. It is a true falling block, with internal hammer. Contrary to most rifles of the area, he also used the stock bolt for attaching the butttstock while keeping the tangs.
Of course, Daniel Fraser made top-quality rifles (and knew very well how to), so that also plays a role, true...
I would personally rate it better than the Farquharson, but for more info - just check the Dehaas book, 'Single shot rifles and actions'
Of course, it isn't better than a Martini

8) ,but it most certainly looks quite a bit nicer. And it has sidelever operation too, making for a very trim rifle/action combination.
Only thing - copying those won't be cheap, I'm afraid, unless you could go to mass-production techniques. Yes, I would also like one, but I cannot afford it...