The most important thing is that the continuity beep is instant. Nothing worse than having your head under a playfield and you can't see the meter and you have to hold your probes for what seems like an eternity to listen for the sad excuse for a beep. They use cheap chips to determine resistance, and tie the continuity test to that. It is a non-zero time to figure out the resistance and emit the sound for continuity. Nicer units will either use a separate circuit for continuity, or a chip that is much faster at sussing out resistance. It really is noticeable once you get used to the instabeep.