I have tried the Nutro and my cats liked it well enough. Right now they are both on the Science Diet Lite Hairball Formula. Upon reccomendation of the vet and Zippy Kat - she said her crew thought it had crack in it!
Kylie still throws one up every once in awhile. She likes the ProPlan treats for Hairballs. I don't use the Nutro b/c I needed something specific for hairball and a light formula as both cats need to lose some weight.
Might try adding a bit of coconut oil or Olive Oil over their food. Maybe mix a bit in with wet food as a treat?
Kylie had a bout of gastritis a few years ago and it was similiar to that except she didn't have a hairball mixed in with it. She had to be on antibiotics for awhile and hasn't had any problems since. **knocks on wood**

And I know you have already bought the Nutro but just wanted to add that I usually buy the NUTRO at the local TSC or Farm and Fleet store. They also have Science Diet but not as big of a selection and of course don't have the lite hairball formula. Only the Light and only the Hairball. :eyeroll: But they are considerably cheaper then the pet store....