I had both of mine done in an outpatient hospital clinic.

The risks increase with people with seizure disorders, or who are already diabetic.

Screening relatively healthy people for trending or fine tuning, is relatively safe. I had a 2hr one done in the OB office looking for gestational diabetes, which was negative.

My second GTT which was a 4hr, I "lost" it near the end. Shaking crying, and pain from the needle sticks and low readings... which my veins created a very painful experience.

Also notice that the website is in Holland... a European opinion therefore. Other countries have different points of view and differing
activities in clinics and offices.
But doing the long test is definitely not safe at home for some patients.
Finger stick testing is less accurate as well, and will not give the same results.

IMO in diabetics the glucose may remain around for a while depending on medication routines. In non-diabetics, it is typically low by the 2 hr mark.