I know all have said skip the kit. I am also one of those.
However, if you look at shroomery, there are some people with good yields on growkits. Soem even reported 300g fresh from one kit alone. thats a LOT. and he was jsut reporting a growlog. It was however quite the kit, illegal in most countries (it was already germinated i think). Generally though dont be expecting more than 15-20g dried from one normal kit. Some other parameters factor in but you should be fine.
There is also the inVitro tek, which grows the mushies in the jars directly, quite easy to hide, very stealthy.... you could also look into that one as it requires practically no intervention.