Hmm I don't know if it's still best also in FSX, but in FS9 it definitly is.
At the moment I can't tell if it'd damage anything because I don't have it installed due to a new FS installation a short while ago.
As soon as I install it (maybe in a month

) I can tell you if it changes any stock files

.
But I never had a problem with it.
BTW: If you don't see a traffic after starting your flight this is because fs needs a while to show you all traffic as the machines all must take-off first.