Yes, Captain Sim does not charge its customers for downloading their bought stuff, unlike some other companies.  >:(

I only had Paypal buys so far and they also gave me the links right after clicking 'pay now' in the Paypal interface.
You then get back to the CS page and see your Order Number and stuff. That's the point where I was able to download, so 'instant access' is present too. Make sure to safe that Order Number, it's vital.
Note that the 737 currently is the external model only, with the default 737-800 cockpit. The full version will come up later.

Your link in the signature doesn't work for me (when clicking), Max.  :-/ There's one 'http/' too much.