yeah, actually I noticed this, they seem to be the only brand to actually add urea to some of their formulas (although the % is fairly small). I really don't know if it is a performance enhancer, or a way to simply cut costs? For AN high prices, I would sincerely hope that their addition of Urea in some of their formulas is for a performance increase.
I speak with Daniel Fernandez every so often, this guy is a hydroponics/chemistry monster. He is the creator of Hydro Buddy software which basically lets you reverse engineer most formulas. Here is his article on Urea in Hydroponics
Urea in Hydroponics – Positive or Negative ?
After doing a study with several concentrations of Urea and Nitrate -both by themselves and combined – this research group found out that
Urea does not improve crop yields in NFT systems and indeed pure nitrate does the best job when no media is in place. When media is introduced, organic media shows a faster Urea to Ammonia conversion but Ammonia to nitrate conversions are faster in inorganic media.
However, the effect of Urea remains poor in the sense that nitrate-only crops outperformed almost all crops except for some plants grown with small quantities of Urea which proves to be beneficial in the same way as small additions of ammonia are already known to be.
So, smack me down and call me silly, but it sounds like AN is cheaping out by adding low cost Urea to some of their formulas, which is dumbfounding since they charge the highest prices.