I have no experience with manufacturer of the stock you have in the link but I’ve used that design of stock. I personally prefer the six position M-4 verson of the collapsable stock. The commercial buffer tube M-4 style stock like supplied on RRA AR-15’s have a longer length of pull than a similar stock with mil spec buffer tube.
I’ve seen the original CAR stock with the appearance in your link with just open and closed positions. I’ve also seen the four position buffer tubes used with the CAR pattern stock. I prefer the larger butt pad on the M-4 stock as it is very similar in shape and size to A-2 fixed stock.
Really boils down to personal preference but link indicates the stock is milspec so the buffer and buffer spring should be gtg.
The stock in the link is very pricey and I’d prefer to use the polymer stock as it is much more comfortable in the heat or cold. Brownell’s list the CAR stock which would be a lot cheaper. Brownell’s is out of stock but can the stock can probably be found at other retailers.