stealthing while in tahm stomach

I was playing tahm trying to squash the way over fed rengar in the last game turning fight i got him ate him and yet i first of all was a bit unsure if i had eaten him because a ! was put on my and my teammates heads he stealthed while being in my stomach. he then gingerly walked up to my ADC and killed him and they won

I dont wanna sound entirely like i am complaining (i am). does this work with vayne, kha'zix and shaco? I thought part of the purpose of Devour was to aid in locking down enemy champs. Not really locking down if they can hide and re-enter fight when ever they want. I think the use of devouring these champs is useless making any great play used to devour them equally useless.