Personally, I don't think there are health concerns using urine for plants. It is essentially sterile.
It has emergency medical uses, with mid stream urine, i.e. suburn, as urea itself is skin moisturising.
As Galatians said, the N Urea content of Urine is far lower than Fertiliser urea, so it can't be used to make the equivalent concentration sprays.
That said, fertiliser Urea has a lot of problems with loss of N to the atmosphere, so often the effective ammount the plants can get is lower than that applied.
Not sure if more frequent low % urine sprays will give the boost of the the N fertiliser Urea spray.
Biuret is produced by heating Urea in the manufacturing process, so shouldn't be a problem in Urine.
I have used diluted urine to feed weak plants or very small seedlings that I didn't want to risk with stronger fertilisers.
Also had some Citron seedlings with what looked like Biuret problems from fertiliser in old potting mix.
It seemed to correct them, possibly by gently lowering the Biuret % in the mix ??