Photography costs. We all know this. So sometimes we can be tempted to save a little money on equipment, but at what cost...?
I've bought a cheap camera strap before (a knock off of the BlackRapid) and I don't rate it. Firstly, it feels like a seatbelt and constantly slips around the shoulder. But this isn't a review, so let's get back to it... Any system is as strong as it's weakest link, and the hang potentially a few thousand pounds worth of equipment from a £20 strap is crazy. And for the sake of saving £30. That's the price of a takeaway meal!
More expensive straps are more comfortable, but more importantly, they are reliable. Some have a metal fibre or cord woven through them too which no only improves the straps strength, but prevents anybody physically cutting the strap from your shoulder and running off with your camera gear.
Not all expensive straps are not, and not all cheaper ones are bad. However, do some research and go with trusted brands if you want to keep your equipment safe.
Your system is as strong as it's weakest point.