I still have one of the prototypes (It has a larger objective than the production units) and had several on my other PCPs before I sold them.

The one I have I now use on a BAR22 (basically an AR15 in .22, not a clone or a plastic fantastic) for CSR practice while the usual optic is on another rifle. This means coming into the aim pretty quickly without poking yoru eye out. There is enough slack in the eye relief for the scope to work without being in firm contact but I guess it depends on yoru eye sight.