Used it on the CB 350F I did this spring and it worked well. The products that I have bought from them seem quite good quality and value overall.
Try removing the front part of the petcock and spraying some PB Blaster in there and soaking for a while. Heat may help too, yet there is an O ring up there that may melt if too hot. I have had a few bowls that were very tight and it seems it is more corrosion than old gas that holds them together.