Yes it’s the gauge only but you’ll get plenty of shots......at least 60 before the low pressure warning appears and a further 20 before poi drop at 100 yards.
Never trust a tiny gauge, always go with what's on the fill source. Never found a tiny gauge that wasn't off. A 250 bar fill isn't going to hurt as the guns been tested far beyond that. Always best to try to stay within the suggested perimeters.