Long term on Methimazole?

Has anyone ever had a cat on methimazole for hyperthyroidism for a long time, like 5+ years? My 7 YO feline was recently diagnosed with hyperthyroidism (I think the vet said level was around 15), I really want to do I131, but obviously it is very expensive. However, my cat is young, I hope she makes it 5-10 more years! That's a long time being on medications that only treat the symptoms. Anyways, anyone ever had a cat on methimazole for hyperthyroidism for a long time? How did they do?