Just my observation...
I was on firmagon for 4 months and 2 weeks ago switched to Lupron. Smarter people than me will add significant info I'm sure, but I'll give my personal experience. Firmagon is very slightly more effective than Lupron and the others in reports I've seen but not signifcantly so. It reduces testosterone very quickly( less than a week) whereas Lupron takes up to 4 weeks. Firmagon does not produce the testosterone surge like Lupron and doesn't require several weeks of casodex before treatment begins like Lupron. Firmagon is injected into the abdomen whereas Lupron is injected into the butt. My firmagon treatments were very painful and my last one hurt for almost 2 weeks. The firmagon has to be prepared precisely and injected flawlessly to eliminate pain. The Lupron shot was given to me by a nurse rather than the Doc and was totally painfree. I relaxed for the shot and had no pain at all. Just my opinion. So, your dad had surgery 2 years ago? If you can provide more info( psa history, pathology,age,dates, etc.), it will be easier for folks here to give more insight.
Best wishes to you and your Dad!