"Better" is in regards to the user's needs/mission. The Comet is a single-port instrument which does scalar (no phase information) reflection-only measurements. If all that the user is interested in are VSWR measurements ("I just want a number!") the Comet is quick and simple. The various nanoVNAs do two-port transmission and reflection measurements and are more versatile, but require more effort from the user in the form of setup and calibration to make a measurement. Either are a quantum leap beyond the old VSWR bridge in terms of convenience and accuracy.
73, Don N2VGU
Donald S Brant Jr