They're probably less lightfast than pigment prints on good paper or canvas, since they use dyes rather than pigments. On the other hand, they're more physically durable.
Dye-sub metal prints are great sellers. With many photos, they are striking and impactful, their Cibachrome-like gloss, intense colours and bold, minimalistic presentation standing out more than less-bold canvas prints, and much more than fragile paper prints hidden behind glass in a frame. But I place great value in longevity, so am always considering other ways to get a bold, lightfast and physically-durable image onto a physically-durable substrate.