.RC. --
You ask a question that I can't answer.
What we in the US call a Master Precision Level (Starrett's Model 199Z is, by far, the most common and most widely known member of that genus, but other makers have included Berger Instrument, Lufkin, South Bend Lathe, Scherr-Tumico, Pratt & Whitney, Queen, Schulte, Taft-Peirce, Universal Boring Mill, and probably a couple dozen more) typically contains a vial in which the bubble will move 1/10 inch -- the distance between the vial graduations -- when the vial is tilted somewhere between 8 and 10 arcseconds. This requires that the inside of the vial be ground and polished to a radius somewhere between 215 feet and 172 feet.
As you might expect, British level vials were traditionally graduated in 1/10 inch increments also.
In contrast, modern European and Asian level vials are graduated in 2 millimeter increments. Having the bubble move 2 millimeters when the vial is tilted 0.05 millimeter per meter requires the vial curvature radius be 40 meters, roughly 131 feet.
In my experience, the makers of precision level vials generally consider a vial to be usable if the measured sensitivity is within 10 percent of the nominal sensitivity. If European and Asian level instrument makers go along with the vial-makers +/- 10 percent tolerancing, a level instrument claiming 0.05 millimeter / meter sensitivity should actually range between 0.045 millimeter / meter and 0.055 millimeter / meter. Stated another way, the vial's radius of curvature should range between 36 meters (roughly 118 feet) and 44 meters (roughly 144 feet).
So . . . the bubble in a standard US Master Precision Level will nominally move 1.6 times as far as the bubble in a 0.05 millimeter / meter level in response to identical tilts. At the extremes of vial sensitivities, the bubble in the standard US Master Precision Level could move as much as 1.8 times or as little as 1.2 times the distance the bubble in the 0.05 millimeter / meter level moves in response to identical tilts.
Yes, the standard US Master Precision Level is a fair amount more sensitive than a level with a vial graduated at 0.05 millimeter / meter of tilt.
Do you need the extra sensitivity when setting up or rebuilding machine tools? My best answer sounds awfully trite: You do if you do, and you don't if you don't.
I'll make a suggestion, though. Go ahead and get started with a 0.05 millimeter / meter level, and when you get to the point that you know you need a better level, you can ask yourself if you can make do with a standard US Master Precision Level or if you need a 0.02 millimeter / meter level.
John