Cheapo Bipod

Attachment 50009

Does any one have or have used one of these bipods? I see they are on trade me for around $20 and they look ideal for what I want.
I have a small rail which I can put above the front sling stud on my stock which it will fit on to and I would carry the bipod in my pack until I get to a shooting point and only have it on while sitting etc.
Are they usable quality and do the legs stay in position when extended?
If these are good why would an Atlas bipod of similar design be so expensive.

Looks like the Chinese have made a copy of the Atlas:
China Hottest! Tactical Military Adjustable Bt10-Lw17-Atlas Rifle Bipod for Hunting Cl17-0019 - China Hunting Bipods, Bipod for Hunting