Navigation, obstacle avoidance, and self-emptying — the big three

Every robot vacuum on the market comes down to three things: navigation (does it map your home or bounce around randomly), obstacle avoidance (does it eat cables or steer around them), and self-emptying (can you ignore it for weeks or do you empty the bin every day). Everything else — suction power, mopping, brand — is secondary to these three. Get those right and the rest falls into place.