Precision <> external finder sounds like an oxymoron to me
The main finder on the sp is very accurate with the moveing bright line projected frames .
In the 28/35 finder both frames are present , there are parrelex lines for the 35 lens which show close up down and to the right .
The external finder mounts directly over the lens so the correction in only vertical . I find this more accurate for framing , and the larger view is a plus .
That is an opinion and perhaps many will differ with it .
The sp is a great camera able to use 6 lenses without external finders , it was nikons response to the Leica m3 .
I shot with an sp for many years in the mid 1980's mostly with the 28 mm lens and the in camera combined 28/35 finder .
I find now that I like the larger view of the leitz 28 mm bright line finder .
Of the Nikon finders the 3.5 cm bright line is the best , the chrome finders are more difficult to use and I don't recommend them .
If you are using telephoto lenses you can not beat the sp , also it has the advantage of the moving bright line for the 50.
The reissue sp 2005 has the advantage of the newest optics and coatings , added to the original design . I had a chance to shoot with one , the finder is just beautiful .
The original 28/35 finder usually has black spots ( deteriation of the black optical paint ) and haze
that make it difficult to use . Many have average rf spots . A servicing makes the difference . However
Even a serviced one is not up to the sp2005 .
You should try the sp it is a great camera.