Make sure you look close at the specs between the Garmin UHD and the Bird Mega.
See Specs from their websites:
Garmin UHD: RMS Watts 500
Ultra High-Definition ClearVü: 0.8 MHz, CHIRP range: 760-880 kHz,
200′ Ultra High-Definition ClearVü
Ultra High-Definition SideVü: 1.2 MHz, CHIRP range: 1,060-1,170 kHz,
125′ to each side Ultra High-Definition SideVü, 250′ total, at a maximum
depth of 30′
Bird Helix Mega SI: RMS Watts 1000
MEGA Down Imaging, MEGA 1.2 MHz (1.125-1.300 MHz), 125 ft (MEGA & 800 kHz)
MEGA Side Imaging, MEGA 1.2 MHz (1.125-1.300 MHz), 250 ft (MEGA & 800 kHz)