I use johnny. But just because i play ST with broover hog, ciri + ciaran. Its almost guaranteed you will combo him with cirian or ciri because broover. Its the only scenario i think he is actually viable though and even so i sometimes get bad "draws" with him.... but hey, nothing can be as bad as a 1 strength card right?
Using him without any of those 3 other cards is just gamble with luck while wasting a silver spot imo.
Another thing that i noticed while using him is that he doesnt recognize premium cards and regular cards as the same card, i.e. if you use him on a regular ciri and your opponent has a premium ciri, there is a chance that you will receive that premium ciri rendering the johnny effect virtually useless... if it is a bug or just an unforeseen mechanic, i dunno.