While I'm a big fan of the GHR you could easily develop the hamstrings for hip extension using RDLs, SLDLs, Good mornings, and single leg variants. If you do have the ability to do it twice a week there's not problem with that but you'd probably benefit from using some other posterior chain exercises once in a while. This will ensure better adaptations and help to prevent plateauing. On the GHR machine alone though there are a couple of variants, single leg, etc.
how often do u use ghr in ur program