Hi,
KB controllers are phase controlled bridges. The active parts are two diodes and two SCRs. They are old school and quite rugged
and KB have been making them a long time and have all the wrinkles sorted out.
The last one you linked to (the first link didn't work for me) is a buck regulator. So there is a bridge rectifier of four diodes followed by a buck regulator
of a MOSFET/IGBT and highspeed freewheel diode. This is a more modern design and can be both rugged, versatile and responsive but at a cost.
Lower priced units such as you are looking at are probably less reliable than the KB types.
In terms of advantages regarding the technology there is little in it, at least for a spindle. The later type PWM regulator would come out on top if you
were modifying it to drive an axis motor but not otherwise.
Craig