The one in your first post appears to slide straight back, on what looks like two mounting points per side.
The ones in your second post appear to have only a single mounting point per side, which has to swivel as the stock is extended. The "lock" appears to be nothing more than tucking the front loop of the stock under/behind the front grip-frame field-strip screw.
Also, the first one has a welded on "buttplate", while the second is just wire. Which style are you interested in?
