I'm not qualified to say whether Methigel is your best bet or if there are other alternatives. Methigel should not be given if your cat has any liver or kidney disease, and should be given with food to prevent digestive upset. If your cat has to be on this medication for a long time, I would consult with another vet for a second opinion, if you are not confident with your present one.

 

You may be interested in this website.
Read especially the "Customers Reviews" .... interesting comment by a vet and others in its use.

Methigel Urinary Acidifier For Cats & Dogs: Pet Urinary Acidifier - 1800PetMeds

 

Since you're giving this per a vet's advice, I suspect that the brand of acidifier is less of an issue than insuring that you are administering as prescribed and ensuring the vet is following up on testing the pH regularly, especially if it's prescribed for long term use. Basically...don't skip or significantly delay a monitoring appointment...if the pH is too low you're risking going the other way and ending up with calcium oxalate crystals.