Phosphate is phosphate. Most people use the home brew recipe because it is about 10x cheaper than store-bought. All do the same thing - produce an iron phosphate coating on the metal. Those two things, degreasing, and phosphating, are the most important. And surface roughing. THREE things, degreasing, phosphating, and surface roughing... I'll come back in.
Degreasing is 50% of the process. Degreased metal is mandatory. Sand blasting, or some other method to rough the surface, will greatly increase the surface area and therefore increase the coat. Those two items are more difficult than the phosphate treatment itself!
And remember, no one expects the Spanish Inquisition!