Nothing beats the optical clarity and 3D ability of the mantis, nothing.
The Tagarno is a top notch digital microscope, but you can't really compare the two. One is stereo optical, one is 2D digital.
The Mantis has two selectable lenses, but the working distance can be a pain at the high magnifications. 90mm at x4, dropping to 55mm at x8
If you are working under is 8 hours a day (as I have done), the Mantis is the best choice, your eyes don't get tired due to the match lenticular distance.
The Tagarno at high zoom suffers from wobble if your bench isn't ultra stable.