I used Synthetix5 recently for a pre-employment test. After a few days the lab called me back and said my urine was too diluted.
Luckily the employer is having me go back for a second test.

Now I don't know if I should try diluting or buying QuickFix.
I don't know if the lab (LabCorp) did some extra or new testing that the Synthetix stuff couldn't pass, or if this brand isn't as good as QuickFix. (and subbing was pretty easy, the lab tech was so busy I'm not even sure they checked the temp).