The quality of the adapter is excellent. I have been staying several of them in daily use. It is never broken one.
For me, the safe installation of eyecup is an important little detail. Unlike other solutions from other manufacturers, the DK-22, FM2 / FE2-Okularschutzglas, DK3 sits combination very safe on the eyepiece and is thus not accidentally lost.
One DK3 eyecup on the D200, D300 ect., Usually covers a small part of the camera display, you intuitively compensated quickly in practice by tilting the housing and there is really no disadvantage.