Read 4U, 5U and G5 as separate specifications. Compare balance and flex using the manufacturer’s own definitions.
Weight class and actual weight
U is a weight-class label. In these Yonex records, 5U has a lower listed average than 4U: 78 g for Nanoflare 001 Clear and 83 g for Astrox 77 Play. An average is not the measured weight of every individual racket. Strings and extra grip also change the finished setup.
G5 describes the grip
The G label belongs to the grip, not the racket weight. All four catalog variants use G5. Try the handle with the grip layers you intend to use; do not substitute a tennis grip-size number for a Yonex badminton G label.
Flex categories
Astrox 77 Play and Nanoflare 001 Clear are Hi-Flex. Astrox 99 Game is Medium; Astrox 99 Pro is Stiff. Use these labels to select the shaft category you want to try.
Balance needs its own measurement
A weight class gives total mass information, not the location of the balance point. A point in millimeters also needs a stated measurement condition. Keep the same strings and grip setup when comparing measured balance.