I don't know if we have just had a really bad experience, but our team has had 4 Grayhill encoders and 3 of them have broken in some way or another. I would be wary. Two were series 63k. Both still work, but the back came unglued from one.
The other two were series 63t. One of them stopped working electrically and on the other the glass code disk somehow broke. That was probably due to a rather rough installation though. In any case, i am weary of grayhill products.