HYS 21-inch NMO Kit with L-Bracket vs Retevis 7.2dBi High-Gain GMRS Mobile

The HYS 21-inch is the clear winner. It's the only antenna here whose performance is grounded in physics rather than marketing.

The critical difference is electrical length. The HYS operates at 0.26 wavelengths on VHF (quarter wave, solid baseline) and 0.77 wavelengths on UHF (full wave, excellent). Its modest claimed 2.15 dBi gain aligns with what that length actually delivers. The Retevis claims 7.2 dBi without disclosing electrical length, which is a red flag. That figure is almost certainly overstated for a mobile antenna, especially one competing on price. A 7.2 dBi mobile would need to be either much longer than typical or rely on a ground plane effect that isn't documented here.

The HYS costs 50 percent less and scores 17 points higher overall because it does what it claims without hype. You're paying for honest performance on both bands.

The Retevis might appeal to GMRS-only users seeking simplicity, but without knowing its electrical characteristics, you're buying on faith rather than engineering. The HYS is the safer, smarter choice for anyone doing multiband mobile work. Buy the HYS unless you operate exclusively on GMRS and accept inflated specifications as normal.