Don't know a lot about them but the Printmaster is based on the GTO. They also make a Quickmaster 46 which is basically a small offset press. I had the privilege of a trip to the Heidelberg showroom in Sydney during my apprenticeship (2001) and they were exhibiting the QM46 two colour press. I remember thinking at the time that you would be lucky to get a decent cmyk job out of one due to the registration system.
The Printmaster 52 is basically a GTO with a bit of a fancy electronics, which is probably not desirable 20 years later. The whole appeal of the GTO is it's lack of things to go wrong. I doubt they would have mechanical issues, probably more likely electrical.
I have a GTO and I love it to bits but it's work scope is very limited in todays modern world.
The Speedmaster is a different kettle of fish all together. Stream feeder, run at 10,000 IPH all day every day. Faster plate changes. Quicker make readies.
Printmaster is slower and more agricultural but I would think no less reliable. QM46 I would steer clear of.
Love to hear the thoughts of some of our senior members