When choosing a flip-front motorcycle helmet, look at the approval label sewn into the chin strap. Under UN ECE 22.06, the number 06 identifies the approval series, while J, P or P/J indicates which configuration has been approved for use. The fact that a chin bar can be lifted does not answer that question on its own.
J identifies an open-face helmet without an approved protective chin bar. P means the chin bar is approved; on a flip-front helmet marked only P, it must be closed and securely locked while riding. P/J means a modular helmet is approved both with the chin bar closed and in the manufacturer-approved open position. With the bar raised, however, the face and chin do not have the protection provided by a closed chin bar.
Before buying, check the label on the exact model and read the maker’s instructions for securing the chin bar. If you intend to ride with it raised, look for P/J approval. With a P-only marking, raise it only when stopped. The helmet still needs to fit your head properly: an approval marking cannot replace trying it on.