He has a point, buying and having the fina carts on hand is legal.
But if you have them and they make the effort to come bust you, your going to have a hell of a time explaining why you have them without some cows, the implant gun, etc.
Also once converted your f*cked. So unless you plan on just leaving the pills in the cart in your fridge, your going to have to cross this line anyways. What if you brew it up and then the five-O come knockin to ask why you purchased the fina cart, they have a warrant and check your place to find a small stash of steroids for personal use. Law is ignorant and they might assume you have enough for distribution since you brewed an entire cart meant for many cows (surely not one human can take that they'd think) bam distribution. Now your in prison.
I will say that many people have successfully done this many times...FWIW.
converting one kit is still illegal but I'd say chances are greater that you will be fine than the chance of you getting into trouble
*-I do not condone illegal activities nor am I recommending doing this.