IM(educated)O they are a rip off. Do not work. As far as marijuana you want to drink a ton of water/gatorade/cranberry juice to flush your system out. I think it helps get the shit out of your fat cells. N then drink a ton prior to the drug test to dilute the remaining thc in your urine. Niacin I believe adds color to your pee so it doesn't look like you're trying to cheat so take it + vitamin B a couple hours prior to testing.
As far as opiates, nothing really works. Drinking water nonstop for days prior to testing is an uncomfortable waste of time. Only thing you can do is drink alot just prior to testing to dilute your urine.
Personal metabolism has ALOT to do with it. Thus some people will swear by certain detox kits because they happened to use one when they were already going to pass the test anyway. Plus gold old flashioned payed reviewers talking up their products.
Save your money. Or don't. I've taken many drug tests under many circumstances, including probation.
Mouth swabs are a joke, I got a mouth swab on probation with my body heavily toxified with opiates. Used 8 hours prior to test, passed.. I kinda of scraped the inside of my mouth and tongue with my teeth before the test and made sure I didn't have much saliva in it.. but yeah I never failed a swab test.. had like 4 of them.
The 5/whatever panel test is the next easiest. If you aren't being monitored U can just put regular water in the cup, peel the flap open and wait for the results to show, then either get it a little wet and flatten the flap back so it doesn't look tampered with, or use a little glue from a glue stick to keep it down. After the results show U can piss in the cup with your own pee so it looks good and is the right temp. After the results display it won't change. If you are monitored.. IDK. Only had one monitored 5 panel and I failed it. (tho it was unexpected so I didn't have a chance to find a way to beat it-- the wizzinator is the best option in that scenario, I think[fake dick with fake pee])
Dip stick test is real tricky. You pretty much need someone elses clean pee. N if you're a heavy drug user, chances are you don't have friends with clean pee n it would weird any other aquaintances out if you ask to buy some of theirs.
but yes buying fake pee is the best only full proof way. Even if you are monitored, you could fill a plastic bag with the urine, tape it under your ballsack and dick, tape a sharp needle or something to your finger and when you whip it out, puncture the bag n let it come out somewhat natural looking. IDK really depends. Some officers act like their life depends on it and literally put there face on your dick while you pee.