primo is a very expensive, often faked, and very subtle steroid. it isnt like tren or deca that produces pronounced results. it is great at retaining muscle and can help build quality tissue, aka muscle, not just increased water retention and glycogen like some steroids. it is one of the more safe steroids with very little in terms of side effects.

realistically what was suggested below, the labmax kit to tell you if its even primo is a good idea. it wont tell you if its dosed anywhere near correctly though. although you will get at least an idea if its primo or not. it doesnt show up on bloodwork, so the only other way would be a mass spec which is very expensive. the other option is to buy pharma primo, but sounds like you already have the primo.

if you are starting a cut at 12% body fat i dont think its pointless to run primo. in 20 weeks with primo you could get down to a reasonably low body fat like 5% or even less if you pushed it hard. you dont diet down to 5% then start primo, you use it for the process of getting your bodyfat lower while keeping the muscle. primo takes 3-4 weeks to kick in anyways. 20 weeks is a long cycle, if your not on TRT. It may be hard to recover from.

more than the drugs your taking matters will be your diet. you cut will be determined by the food you eat more than the drugs you take. when i personally ran primo i kept test high and did just fine, just make sure you get bloods done at 4-6 weeks into the cycle and make sure estrogen is in check.

I think you could do well on 400 mg/week primo

That's a long cycle. Unless your on trt already. I would love to run primo but I just don't see my self running such a long cycle as of yet or maybe ever. Due to length of shut down.

Definitely drop your test as was said already. I like to run mine around 200 with primo. That much test will still cause you to convert estradiol and ruin a bit of that primo look for you. It will really shine as far as polishing you up while holding onto your muscle. It's by far the most aesthetic look of any compound I've run including tren. Makes you rounder while more cut while tren tends to make you too flat and grainy in my opinion. Also got some insane vascularity while using it personally.
As for what sides to look for:
The whole point of primo is that the side effects are non existent. Really all you can try to see is that look I mentioned above, along with strength and tissue retention on a cut. If you're concerned about the authenticity then as said already, invest in a testing kit. Feel free to message me for anything else I can help with and good luck

Not that familiar with primo but I don't think there are any ways to tell its potency visually. I would say your best bet is investing in a test kit. I would advise testing it before you ever put a foreign substance in your body, like you said primo is a compound that is often faked.