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Just take a look through a long focal ratio Classical Cassegrain or Maksutov with a small secondary - at least f/12 to f/15 - to see what it's like.
There's not a lot wrong with a long focus Newtonian apart from size, however there is an issue with making the secondary large enough to fill the field of view of a low power eyepiece without too much vignetting.
I made a 6" f/18 folded newtonian in the late 1970's in an era when high power eyepieces were truly awful... it worked pretty much as expected, lovely high power images but there was really only high power...
IMHO with the improvements in eyepieces in the last 30 years, f/15 is a bit of a waste and f/8 is the ideal focal ratio for a Newtonian. Secondary is small enough not to matter, but still capable of low power if you have a 40mm eyepiece.
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