Studies to measure the actual absorption of B12 involve wholebody counting of radiolabeled B12, counting of radiolabeled B12 in the stool, or both. No data are available on whether B12 absorption varies with B12 status, but fractional absorption decreases as the oral dose is increased (Chanarin, 1979). Total absorption increases with increasing intake. Adams and colleagues (1971) measured fractional absorption of radiolabeled cyanocobalamin and reported that nearly 50 percent was retained at a 1-µg dose, 20 percent at a 5-µg dose, and just over 5 percent at a 25-µg dose. The second of two doses of B12 given 4 to 6 hours apart is absorbed as well as the first (Heyssel et al., 1966). When large doses of crystalline B12 are ingested, up to approximately 1 percent of the dose may be absorbed by mass action even in the absence of intrinsic factor (Berlin et al., 1968; Doscherholmen and Hagen, 1957).
From Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline (1998)Chapter: 9 Vitamin B12
Side note; GFuel has 10-µg per serving which is well below any dangerous limit (upwards of 2,000 μg)