I bought a Yong Heng clone to fill my PCP about 2 years ago and it's been absolutely fine. As long as they're not overstressed and you change the oil regularly they're just the ticket for filling a rifle.
Extra filtration is needed, such as the Airmega inline oil/water filter that costs about £35, which is perfectly adequate and what I use.
I recently took the filler valve out of my rifle to change a leaking seal and there wasn't a drop of water in the cylinder after 2 years of filling with the above setup.