They didn't work for our little Piggy Marie unfortunately. We tried the hormone injections and the implant before actually going through with a spay. I would never recommend the implant again though - I think it has subsequently been proven to be ineffective and is very expensive. Unfortunately it is almost impossible to tell how a piggy will react to hormone injections until she has them.
They didn't work for Piggy Marie, largely I think as her Cysts were very large. Our vet says she always recommends a spay over the injections as she always strives for a 'gold standard' of treatment and care and injections are just too variable. Given that a spay is a lot more work, higher risk and cheaper than the injections, she isn't just saying this to make a quick buck.
That said, depending on the age of the pig and the size of the cysts, I would still consider hormone injections in the future.
I also know the feeling of coming all at once, with seemingly never ending bills so I do feel for you.
Good luck with your Piggy problems - and you are right this Forum is great.