I had to make that choice one with my Peanut (dog), in his case it didn't work because his illness was of a different nature than Benni's. Peanut was a victim of a mysterious immunologic disorder that make his immune system depressed and he wouldn't eat, he was hospitalized for about 10 days and at some point the vet talked to me about the tube. I said yes because I wanted so badly to do whatever possible to save him.
Now about the tube itself it does the work, Peanut's was on the side of his neck/shoulder they keep it covered until food is inserted.
It doesn't look as brutal as I imagined. I think if Peanut had a chance the tube would have been a good thing for him.
I don't know how uncomfortable that could be for them and emotionally.
" How we behave toward cats here below determines our status in heaven."
- Robert A. Heinlein