Here's the thing. Genuine test boosters do not suppress natural levels. If, by some lucky chance, you're natural output is already optimal then not a lot will happen. If, however (and is all too often the case), your levels aren't quite what you'd want them to be then a test booster WILL help.
Now understand the following:
Age makes a difference. It's perfectly normal to have lower levels as you get older. Else you'd see 90 year olds chasing skirt.
Stress can and will fuck with natural production. Reduce stress and you'll see an improvement.
Ditto a lot of drugs.
Not getting enough sleep... piss poor diet... working like a mofo... yep all will lower test levels.
And (as per a couple of articles and their 'results'... if the test boosting product is NOT a test booster but a PH or even a PED then yeah it's gonna lower natural production. Well d'uh.