I honestly think it's the hardest guard to master. Bc we all learn it in the beginning. At least most of us do. But everyone pretty much knows what's going on so you really have to master the position. I actually prefer closed guard over other guards. With the exception of butterfly. 
Rock the Gaspare -They mean avoid falling into the closed guard while on top; not avoid playing it while on the bottomTrevorRice - "Closed guard is hard to even get"Its funny the Mendes Bros always say avoid closed guard at all costs. I always go for it lol
-agreed. I often wonder how BJJ players in the 1960's would play guard. Not alot of open guard options etc. must have been interesting to see.
Today ?
Liera jr, dan covel , Abraham marte, mike perez, calasans jr , paulo miyao , joao miyao , murilo santana has an awesome game built off the brabo grip from closed guard, gezary matuda , daniel beleza , xande , roger gracie
Rafael barata and dan covel changed my closed guard game forever