It really depends... which/how many pets you want to stat and how you get those Scratchcards.
If you buy those Scratchcards with Dukkas over time and not on SS then it can be worth it.
I have one high stated pet, which takes ages in the Gym and some semi stated pets, so it is worth it for me. If you only have one none/low stated pet then the Gym is still best way to go. If you don??t care how much mps you have to spend, you just want stats fast then boosters would be the best advice I could give you.
I am intending to go on with it.