Nought has hit it on the head, 2 units of 5 are much more useful.
Thing is they're not pistoliers and don't work well being used in that role, they are fire support and need to be kept out of harms way if at all possible because they're expensive and have minimal armour, 10 of them is free points to a canny opponent. Vanilla unit of 5 is great (muso if you must) as point for point they outshoot handgunners.
Vanguard should be used to get your outriders into: 1) a better position to fire, 2) out of harms way, so forward I not always the best option. If you can get them into a position were they can fire on the enemy as they advance but out/away from the enemies charge arc great, otherwise vanguard just into range, blast away for 2-3 turns and run away.
Another option is make the most of TLoS, park them behind other missile troops/infantry and shoot over their heads
Move and shoot is limiting, but plan ahead and they'll do alright
Middenheimer