There main purpose
kommandos are primarily there for a surprise attack unit and are very good at popping up and causing as much mayhem as is possible before they get a thunder-fire cannon shell in there asses.
you want to aim for your enemies units that are worth over 200p as this is around the size of unit that the kommandos will get there points back for killing em. and even then once they've got there points back you will probably have plenty boyz to spare and maybe blowup a few tanks on the way to contesting an objective
boss snikrot
snikrot is there to give the kommandos squad extra benefits such as.
he and his squad can enter from any table edge if held in reserve.
if the enemy unit in combat with the kommandoes unit loses and has to take a moral check. then they suffer an additional -1 penalty to there leadership.
id personally prefer a nob with a powerklaw and boss pole as he is cheaper and adds some serious anti- tank.
squad size
when it comes to orks the bigger the better

take kommandoes in squads of 15. then your fearless, if you happen to get shot by a bunch of small arms fire. also 1boy=4 attacks so youl want lots of em
Alternate models
if you want cheap kommandoes id reckomend buying at least 1 box of em for the nob with the klaw nd the cool looking boyz, then just use ordinary boyz with stickbomz and a few weapon modifications
(chain axes aren't so good as if you were a kommando you'd want to keep quiet)
What armies hate them...
mainly mechguard, tau and even nids don't like em that much. because if your entire tactical reserve is to run away and shoot from afar. then all of a sudden you have a kommandos axe in the back of your head you wont be to happy.