when i did my bov it literally took me 15 minutes to put in, very easy!!
also with my 05 wrx i have had NO problems with how it has ran since putting in the bov, but do make sure whatever bov you do buy has the proper plug for the recirc line, i helped a fellow member put one on today and he didnt have the plug, so i made him one to use.
his car also runs just fine since the install and he has a 02 wrx.
good luck and if any questions on the install let me know.