Maximum effective ISO is an estimate of the highest sensitivity at which a camera can capture excellent quality photos.
Cameras with higher effective ISO will be better choices for indoor photography, night shooting, and indoor sports photography, especially if you intend to make large prints.
You can learn more at our glossary entry.
Maximum effective ISO test data courtesy of DxO Mark.EOS M5 test data on DxO Mark GX85 test data on DxO Mark
Excellent build-quality; Good ergonomics for its size; Built-in 5-axis Dual IS, Built-in EVF; Tilting LCD touchscreen monitor; Competitive still image quality; Excellent 4K video quality; Fast autofocus and burst modes; Generous buffers; Tons of advanced features; Built-in Wi-Fi.
EVF could be better; Sluggish RAW and RAW+JPEG buffer clearing; No external mic and headphone jacks; Slow x-sync speed; Mediocre battery life.
Enthusiast-oriented compact camera body; Good image quality in most situations; Built-in electronic viewfinder; Impressive Dual Pixel CMOS AF; Very good overall performance.
High ISO image quality and dynamic range aren't quite up to par with some of its competition; No 4K video recording; Native EF-M lens selection is still limited; Below average battery life.