Personally I like the single-sided bungee because I find that with a double-sided bungee if you're not careful the potential is there to slingshot the butt of your weapon into your face (if your weapon caught on a branch, let's say). This is less likely with the single-sided variety. The bungee is there to pull the weapon in closer to you when you have it stowed, yet allows for it to be extended when you transition to a weapon ready position.
The main reason I went from a 3-point sling to a single point is because the stress of mounting to the weapon is at a single and relatively strong point, the point where the receiver and stock/buffer tube meet. On a 3-point (or 2-point), part of the mounting is at the front end. For airsoft weapons this can become problematic over time due to the amount of stress it places on the connection between the barrel assembly and the receiver. You definitely don't want to use this type of sling on a plastic body. Even metal bodies can fatigue over time since they typically use much lower quality metals in their construction. These are technically toys after all, they're not really meant to be abused (as much as we tend to anyway).
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