They are good. No reason not to use them....
The thing is that it's not really a suggested starter gun. They use the expansion of gas (propane/greengas/duster) - don't worry it's perfectly safe unless you have a lighter right next to the ejection port and actually try to kill yourself and even then it's pretty hard - to propel the BB and also cycle the slide this gives a "blowback" action which adds that much more realism which is why people get them.
Can't comment on HFC specifically but the big names to look out for are KWA, KJW, KSC, WA, TM, etc.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE