I have a Tamron 500mm that is really quite good indeed, found as a used bargain. There is a lot more in the optical design than in a typical Maksutov. The additional constraint to provide a flat field for 35mm film means that this includes corrective optics - kind of an "Edge" Maksutov if you will. The trade off will likely involve "acceptable over a wide range of focus lengths" (down to about 6ft for my example!) rather than the telescope with the single constraint of correction at infinity.
Used on my crop sensor SLR, the results are quite impressive. It's also easier to carry around than a conventional long lens. Pros and cons of course - there is no aperture control (fixed at f/8), and also the issue of out of focus highlight "doughnuts".
I've played with my 127mm Mak a few times in daylight, as a 1500mm camera lens! Focus is tricky to control in perfect conditions, and the image scale easily reveals thermal disturbance. However, it can work well if the conditions are right. Baffling/stray light control was initially very inadequate and contrast quite dramatically affected by this. Flocking the baffle tube made a vast improvement - there's a thread somewhere in Cats & Casses in which I presented pictures documenting the effect on image quality.
I must have another play around with this