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I regularly imaged with a F/5 Newtonian that had a dew shield extending nearly the full length of the scope so the secondary was in the middle of the tube like your photo. To me is it's an advantage because the secondary is encased in the tube so no dewing and no stray light. At F/4 I doubt very much you'd get any kind of vignetting with the aperture if that's what you're worried about.
PS: The only down side was it's more likely to get caught in the breeze with the extended front. But then again when it's windy there's not much you can do about it.
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