What's the difference between higher-end and budget Roomba navigation systems?

Higher-end Roombas (i3, i7, j7, s9) use camera or lidar mapping to clean in neat rows and allow no-go zones, while budget models (600 series) still use the old bump-and-run navigation that goes straight, hits something, turns, and repeats. The budget method works but takes twice as long, misses spots, and can’t be directed — mapping models are worth the extra cost for intelligent cleaning.