I'm sure it goes without saying..lol.....4lbs per K is only a baseline. A truely knowlegable professional would apply per specific need and situation. EX. if you are feeding an under fed area, the 50% quick will win EVERY TIME..to a layman that is. If you are feeding a well fed area...the 50% quick will LOOSE EVERY TIME...when compared to 16-2-3...too much growth etc. I have my 5 acres down to a science...great color..very little growth. 16-2-3 and 7-2-12 are the products I use to achieve that, and only because I tried all the standard lesco type stuff first. Keep in mind I used standard syn fert for 18 or so years. Many companies are starting to sell similar products to Barry's because they offer a higher level of turf control....plain and simple. I often speak with golf supers around my area (luckily some of the top nationwide) and they are all using a wide range of products....none of which is a standard syn 50% scu or xcu. Most in fact are using products that are similar to what Barry sells. I'm not saying that as a commercial lawn company you should use this or that...only that if you are trying to fine tune a turf enviornment 30-0-5 50% xcu is just not something that would be used.