Even against try hards that headshot you within seconds I managed to get some of these kills within one single game by just running around with a smoke bomb in my hand. (I played private against friends and the skill was more useful in 2vs2 than its in 4vs4).
But if it is possible to suprise them and get a few smoke shiv kills in one single game it should be way easier to get them on noobs. However it is true that its more or less a thing of luck, either you get the shiv kill, survive with some health left, or you die yourself and waste a bomb.
And against a team of 4 good players that protect each other its way harder to get it to work.
I think 5 points are a lot for the possibilty of maybe 2-3 easy kills that still need to be executed well, this skill is never OP.
Also its very likely that you will get killed aswell if there is more than one enemy around he just runs behind you and shivs you as well.