Drop-in additives like the Urineluck will not work on instant-type tests because it takes 90 min to fully destroy the drug metabolites in a urine sample.
Also, labs are detecting additive use on a more frequent basis than ever before. They are detected when the sample is flagged for excessive nitrites, high chromates, and/or an abnormal pH.
Youre better off sticking with the synthetic sub. Its easier to pour a sub in a sample cup than holding the sample cup (filled with urine, I may add) with one hand and fumbling around with 2 additive vials with the other hand while in the bathroom stall.