Cheap airsoft ones are very flimsy.  I used to run what I think where better made but still airsoft ones.  I found them useful on milsim weekend games or resting your gun  when in a building or defensive position. Saves you from putting it down in mud and also keeps it in a semi guns up position, especially if you in prone position lying in ambush.  However they are huge as a vert grip, i prefer the Magpul MVG.