As a vet who sees a lot of cats, Cerenia is one of the most common drugs I turn to for cats these days.
It is far superior to many of the other anti-emetics used in the past. It is nice in that it also has some anti-inflammatory properties particularly good for conditions such as pancreatitis or rhinitis.
It is true that the tablet form is widely used off label in cats in the US. The injectable form is labelled for cats.
I have yet to run into any major adverse effects in cats from use of oral Cerenia. A number of my patients with chronic pancreatitis, kidney disease, or gastrointestinal disease, are on this medication at a low dose long term, and it really does seem to help.
Some cats are particularly averse to the flavour of the tablets (foaming and drooling, which usually subsides within a few minutes), while others don't seem to taste it at all - not sure how to explain it!