I notice it within an hour or two of taking it. Take it right after a meal. You will feel like you are digesting it way slower than you normally would. Literally a couple hours later you will feel as if you just ate 10 minutes ago.
Is it worth it? Absolutely. Low risk profile and can be found for cheap. However, I doubt you are legitimately plateaued. Are you sure your calorie intake is 100% controlled and you are consistently doing cardio? Just "eating healthy" isn't gonna make you lose weight dude. You can eat healthy in a surplus. That being said, if you are having trouble putting the fork down, GLP-1s are useful. Other GLP-1s like tirzep or reta are possibly better but I don't have personal experience
As for source, I don't imagine this compound is commonly faked. You can judge if its legit based on the effects alone. If you are not noticing appetite suppression or sense of fullness, especially as a new user, that shit is probably completely bunk or deteriorated due to age/poor storage. A source might be underdosed but completely faked, I doubt it.