It's useful as a one off tech definitely. But garb is still better at its job.
Free poison is good in the early game for decks like toxicroak, raticate break, etc. So it's a good inclusion in poison decks.
As far as competetive goes it can tech against the new giratina which might see play later on. It's a good substitite for silent lab. I would definitely put it in a deck where you utilize abilities on stage 1 or stage 2 pokemon, then use alchemy to deny an opponents setups from their basic abilities shaymin, hoopa ex, volcanion ex.
Many new abilities that will see play are solgaleos free switch, and decidueyes feather arrow and those abilities are very powerful. Alchemy will not stop them.