I prefer the term, "spot Maksutov" because Gregory did not invent that idea. It dates back to Maksutov's original work - but it didn't really gather interest until Gregory promoted it with two specific versions: 6" f/15 and 23 in 1957.
"Maksutov" covers all designs that have that steep meniscus in front to magically correct for spherical aberration without adding much color - and that includes Newtonians, Cassegrains with spot on the secondary, Cassegrain with separate secondary - etc. And "Maksutov" doesn't need to imply spherical surfaces - but he did promote an advantage of the design as having spherical surfaces - but in reality that didn't make them easy to make - or make well. That's why they tend to cost more - especially the good ones. They are in a class of design that relies on final checks of the assembled system to allow final corrections to make sure it works well - and both Maksutov and Gregory describe the importance of final figuring with an autocollimator.
The need for asphere depends on the operating f/ratio, the speed of the primary (and length of the tube), the thickness of the meniscus, and the aperture size.
If you see a current spot Maksutov offering that is 6" or larger and below f/15 and in a relatively compact tube - and it isn't optically horrible - then it probably involves an asphere as part of the design. The smaller ones may also involve an asphere, but it is easier to be diffraction limited when the aperture is smaller. They may also not be operating at either the stated aperture or f/ratio.