I bought my son the ECS10 for Christmas. It only came with 10 darts - which I can guarantee will be lost by Christmas lunch time!
Was looking around and found the X Shot 100 dart pack for half price (£5) in tesco with free click and collect :)!
My son has a few of these guns (nerf and X Shot) and the bullets are compatible across makes :)!!
I am very much looking forward to having to hide all day while I he tries to shoot me with them!!
(Oh and these tips aren't as hard as the nerf ones so they hurt a LITTLE bit less :) !)