It's a lie, mushrooms are like weed. No 2 people will grow the same. Many different things come to play inc user skill and/or experience. To say 500-600 is just a stunt to get you to buy them. Just like grow time and yield from seed companies.
Growing your own is easy and simple. It take literally 15 mins to do. I use a method with corn flower and vermiculite. 50/50 mix into jars. Tin foil over the top. Sterilisation and inject. I make my own beer and I wish it was that quick and easy.
It's also worth saying that once you grow some you can create your own syringes. Something a kit can't offer you. Enjoy the shrooms and you can grow the same one forever.