I would assume your talking about ANSI pumps that have bearing housings with rabbet fits to accept c-face style brackets for mating c-face motors?
If so, they would help with the cost of having to align a motor via the traditional laser alignment method. It has the benefits of close-coupled pumps, but I'm not sure how they ship from the factory. With spacer style couplings (traditional long-coupled pumps), you can verify rotation of the motor without having to disassemble the whole thing (as you would with close-coupled units). As far as vibration, I'm not sure - they weren't the fad at the paper mill I worked at during my preventative maintenace years. It does limit your coupling options, and can get tricky getting the right baseplate.