The audio quality is excellent, thanks to VTech's use of DECT 6.0, so you shouldn't hear any interference, static, or echoing when you listen in on your baby. Since the monitor uses a special frequency to relay the signal from the monitor in your baby's room to the parental unit, everything is encrypted and secure. No one but you will hear your baby.
It really depends on what you feel most comfortable with. There are audio monitors that allow you to listen to any noise coming from the nursery, vital monitors that track sleep and breathing and video monitors that add sight to sound. Babylist parents overwhelmingly choose video monitors. The security of seeing what your child is up to—like if they’ve gotten tangled in their swaddle, pulled their diaper off or climbed out of the crib—can be worth the extra cost of a video monitor.