Well, I've used the good ol' meggers quite a bit, hand-cranks, battery powered etc., and they work well for finding insulation (dielectric) failures primarily.
The unit you linked to looks like it performs some farly simple straightforward tests, based on pulsed or A/C measured winding impedences. There are other testers available also. In my own experience, for users of motors (as opposed to motor repair facilities), when a motor doesn't function properly it can be found with a multimeter and megger. The item you describe seems to be a handy device, but not for finding problems with the motor circuit itself, except very indirectly by learning a bit about failures of motors connected to any particular power circuit when (or should I say "as") they fail.
It looks most useful for determining the condition of "used" motors, or as a final quality assurance check of motors that have been rebuilt/ repaired/ rewound.
Be certain that any such unit you buy is well built and warranteed by a reputable manufacturer. If it breaks, becomes unstable, gives questionable readings etc. you need to be able to verify its correct operation.
remember: An opinion is only as good as the one who gives it!
