The Houghton design and other derivites of the primary corrector at the focal plane area are known well enough but they, like anything other than the Newtonian design have manufacturing flaws that need to be overcome.
The problem specific to the Houghton is the construction of a pair of lenses of weak power of the aperture of the primary. These lenses are sensitive to the proper sphericity of the surfaces at the speeds used by the astronomy community - look at the shape and depth of the Schmidt Corrector plate for the same spec primary and you will see what I mean.
Please don't take this to mean that the Houghton design in any of it's flavors isn't a nice scope - I've looked through several and they were excellent scopes - but rather, like any other scope, it has it's own set of problems that needs to be solved and one of those problems is the 4 optical surfaces which need to be coated in order to not reduce the light level to low levels.
Thanks for the report on the scope.