I have never used them before so I can't comment. I personally use the approved sources on the board - ag-guys.com, sarms1.com and n2bm.com
SARMS, SERMS, peptides, weight loss drugs and PDE5 inhibitors are all controlled substances. What that means is that they are only illegal if you do not have a prescription for them. There is a legal loophole however. Companies can legally sell these compounds without a prescription as research chemical liquid. All the company selling the products needs to do is put 'for research purposes only' on the website selling the products.
The problem with this is that compounds sold for research purposes aren't under the same regulations by the FDA as supplements and drugs are. The company can basically put whatever they want in the product and legally sell it as long as they put 'for research purposes only' on the website.
As a result, the market is full of fakes. If you don't want to use the approved sources on the board, do your research before purchasing from any of these websites.