The base m is compatible with the aton m and sirona m2 i size due to the individual adjustable isofix connectors as well as the height adjustable load leg the two car seats gains extra stability and safety on the base m the one click installation offers a safe and simple installation that requires no further fastening installation indicators also help to prevent a possible misuse compatible with the cybex aton m and sirona m2 i size r129 i size compliant with the sirona m i size r4404 co