GFCI outlet on 2-wire ungrounded question
(NB: I'm not an electrician, just a homeowner who has done some electrical work)
Related: Does a non grounded GFCI meet code?
It is 'perfectly acceptable' in that it is compliant with code (as long as it is properly labeled, as you state). A GFCI if wired correctly should trip if there is a difference between the current coming in and the current going out (between the hot and the neutral, basically).
However, you are right as well that there are dangers/disadvantages to not having a ground wire. The point of ground wires (and requiring them in new construction) is because it is safer both for you and for the equipment you have plugged in.
Without a ground, a lightning strike or other power surge can seriously damage you (if you are touching a plug or outlet when it occurs) or your equipment plugged into any ungrounded receptacle. Ground wires act as an 'escape route' for extra current to travel safely back to the actual ground underneath your home.
Millions of people lived for decades in non-grounded homes and never had issues. But many people have experienced shock or equipment failure due to said lack of ground. It's up to you if the threat of power surge / lightning strike ruining your equipment is an 'acceptable risk' or not.