Are you sure, RW? I can't remember the last time I heard of someone discovering a comet with 7 power binocs. A lot more people are doing it, nowadays. So by the time you could pick it up with smaller binoculars like those, chances are someone else with better optics would've already found it.
Each lens of the 20X120 binoculars is almost 5 inches in diameter for good light-gathering. 20 power also means the field of view is somewhat limited compared to 7X50 binoculars, but still greater than most telescopes. Compared to ordinary 7 or 10 power binoculars [7X50 or 10X50,] the 20X120 binoculars have plenty of power and light-gathering ability; perfect for comet finding.