All supplements with Cystoseira Canariensis extract (the famed CSP-3 patented compound in MyoStim and Myo-Blast) do not work.
Here's proof: Entrez PubMed -- it took me hours to find this medical study, titled
Effects of an alleged myostatin-binding supplement and heavy resistance training on serum myostatin, muscle strength and mass, and body composition..
Briefly: the abstract of the study says:
This study examined 12 wk of resistance training and cystoseira canariensis supplementation on serum levels of myostatin and follistatin-like related gene (FLRG) and muscle strength and body composition. Twenty-two untrained males were randomly assigned to a placebo (PLC) or myostatin binder (MYO) group in a double-blind fashion. Blood was obtained before and after 6 and 12 wk of training. PLC and MYO trained thrice weekly using 3 sets of 6 to 8 repetitions at 85 % to 90 % 1 repetition maximum. MYO ingested 1200 mg/d of cystoseira canariensis. Data were analyzed with 2-way ANOVA. After training, total body mass, fat-free mass, muscle strength, thigh volume/mass, and serum myostatin and FLRG increased for both groups (P < 0.05); however, there were no differences between groups (P > 0.05). Twelve wk of heavy resistance training and 1200 mg/d of cystoseira canariensis supplementation appears ineffective at inhibiting serum myostatin and increasing muscle strength and mass or decreasing fat mass.
In other news: there exist myostatin binders that do work. But they're undergoing tests as drugs for muscular dystrophy patients only, and thus their availability in the market (either black or legit) is nil.
Now, please don't take my word at face value. Go read the study and draw your own conclusions.