Although I concur that a +3 BS in a five man team is juicy and in TAK you can do it is cheaply to buf a Vet Kazak, there is an argument to be made for a Haris team over a full core team. - Maneuverability: moving 5 men on one order is pretty order efficient. But moving them across the battlefield might be hard with finding a save route and cover for everybody on the team. 3 men might move way easier across. Especially if they are made for doing objectives. In my own experience I prefer a 5 men team to go defensive, but a 3 men team to go offensive and cross the battlefield. With 5 men you might end up in a conga line, easy pickings for a blast weapon. - Limited Insertion. If you can bring only 10 men, it might be a smarter approach to make the team more diverse and stick to small link teams to have room for other units. Spetsnaz, Tankhunters, Dog Warriors and Antipodes are very juicy to just pass up on. - You are a crit God! +3BS is wasted on you since you can even roll the 2s when in a pinch.
Just to throw my US two cents in, I frequently run a full core and Haris in most of my lists. Granted, I don't have the sheer firepower of vets to spice it up but a two sniper, paramedic, rifle, flamethrower core does wonders for holding down my DZ. Especially when complemented by a three man Marauder Haris with BSG and Molotok. Points wise that's pretty similar to a Frontie Haris backed by a Kazak core of cheapies buffing a vet. The Haris is far better suited for maneuvering upfield but the five man is just so strong in ARO and Active turn for defensive work that they work well together. Especially when you consider how order efficient it makes the rest of your army.
