Most private label products are the exact same or nearly the same formula as the branded product...but not K-Gro. It is significantly different. Miracle Gro has a lot more nitrogen in it.
I almost always buy the private label product. For example, Weed and Feed is a great product. But I have seen much better results from Miracle Gro than K-Gro and now refuse to buy K-Gro.
I have to say, after living in FL and buying K-Mart's potting soil, yard dirt, and fertilizer, my nice yard is full of weeds that starting coming from the dirt I bought as K-Mart brand.