Question regarding PowerFULL + other sleep aids

[Headphon3s]

Hello, I recently bought a bottle of PowerFULL, and have been taking it according to dosing instructions on the label, and I was just wondering if there were any adverse effects to stacking it with a product that contains phenibut/gabba. The guy working at GNC said to be safe not to take both, since PowerFULL is supposed to help with sleeping, but I was just looking for second opinions.

Also, since PowerFULL is being dosed on a 5 on/2 off schedule, would it be alright to take the other product during the 2 days off?

Thanks in advance, sorry if the question is noobish/stupid