OK , Here's my best answer for you and everyone who might want to ask the same question ... The higher the frequency response the better the sensitivity , I hope I worded that correctly .. And the majority ( if not all ) made exclusively for metal detecting have a 15 -20 frequency and volume controls , some have sound limiters to protect you hearing and all are built sturdy but sometimes can be uncomfortable .
Now you have to justifiably decide what your needs are and if the price tag is within you budget . If you want to pay extra for the limiter switch and durability you can by a pair of Sun Ray Golds for a mire $130 new .
Or if you just want a nice pair of headphones , any brand with the same frequency and volume controls on the cups will do fine . And those can cost from $25 to $50 . I hope this helps you decide what you want ... IMHO , Woodstock