The concentration curl is not necessarily overlooked, however – it is often misunderstood.
I often see people try to perform this exercise while bracing their arm by resting their triceps on the inside of their leg while seated. Although this is not a “bad” exercise, it is useful, it is NOT a concentration curl. This would make it sort of a unilateral preacher curl, but without a preacher bench. It still creates muscle damage and engages the bicep, but not in the way that the concentration curl does.