I can't speak for mumbles but I know a lot of people don't like them because some of the products are absurdly toxic...and more or less over the top....not to mention overpriced. In terms of potency and quality though I personally feel like it's safe to say they are the real deal.
What product do you feel is absurdly toxic?? Metha Quad? None of their products are over the top in any way - I think a lot of people get this ridiculous bro science idea from these forums that stacking methylated compounds is gonna kill you dead on the first dose. People love to crank the dose as high as possible as fast as possible on a single compound, but they'll crucify you for stacking Msten & DMZ. Well take 50mg of just Msten/day, and take 20/day stacked with 45mg/day of DMZ and tell me which one treats you better. On the 2nd option, you're gonna get darker urine, some back pumps, cramping, prob heightened bp, get winded easier, big increases in muscle fullness, lean mass gains, strength-endurance and significant hikes in sheer power. On just 50mg of Msten solo, all of the negative sides will be probably 3x as bad and the positives will be half as good. Your liver will literally be aching, and you could end up in the hospital quick.
With steroids it's often 1+1=3, and large doses of 1 compound tend to just increase sides much higher than increases in effect. Synergy with more moderate doses of a stack of compounds is both more effective AND easier on the body. Metha Quad is literally lower side AND more potent than a bigger dose of just one of those compounds.
Sorry if that wasn't what you were trying to say; I just don't want people to get the wrong idea - I used to believe the whole "don't stack methyls" bs until I just tried things for myself and realized the bloodwork doesn't lie.