DeHaan guns are made by CZ (Huglu if you are looking on Shotgun World) but are produced in a separate part of the factory than the normal CZ-USA products. They are made with slightly more hand fitting and a higher attention to detail than the CZ and are done to custom specs including stock dimensions (if requested), the grade of wood, stock style, metal finish, engraving style and other options. He orders them from the factory and when they arrive he goes completely through each gun and hand fits/polishes all components where necessary to assure proper and longterm service.
Owning both a normal CZ and a Dehaan I can attest to the higher quality of workmanship with the DeHaan. If you look online you can see some examples of 4X and 5X wood on some of his models which makes an absolutely beautiful gun that functions very well. To that end, Mark (DeHaan) also services his guns if something arrises and he is renowned for very good work and extremely fast turnaround. He stands behind his product!
That said, for a nice SxS without looking at used pieces like a Parker, LC Smith or similar the DeHaans are hard to beat for the price (Especially in sub gauge guns). But in an O/U unless one needs stock dimensions that are way off of standard you might be better served to look at something like a Beretta Silver Pigeon for the same money.
"Shoot low boys...they're riding shetland ponies in search of true grit" Lewis Grizzard