My neighbour (7yrs old) owns a nite finder, it's a decent gun for the price although not one of nerf's finest. After a while, the gun stopped working- I am the only one out of all the kids on our street that can use it. This is probably because of the spring and plunger mechanism inside the gun, when you push a whistler dart inside, it almost instantly juts back out, so nothing fires when the trigger is pulled. For those who experience the same problem, there is an easy fix of lightly placing your thumb or index finger on the dart's side to keep it properly inside the barrel.
Note: after about 15ft, the dart veers off to the left or right depending on which side you place your finger, I recommend that you buy and extra pack of whistler darts as three darts will never be enough. I am a large fan of nerf so I find that the Nite Finder is slightly disappointing. But remember, it's nerf or nothing ;)
BUT for an extra pound or so, I think that the Nerf Maverick is better- it works equally well with every dart and has a rotating barrel of six darts- and cocks easily for younger users.