Are you looking for impact swivel sockets or are you asking about regular impact sockets and impact universal joints?
I think the Napa impact sockets and sunex are very similar but, not exactly the same. You can probably find a sunex set cheaper online but, buying a NAPA version would allow for warranty service at your local NAPA Store in the rare chance that you needed it.
As for impact universal joints, I find all of the Taiwan made versions (Grey Pneumatic, Sunex, NAPA, etc.) to be fat. They work ok, but, their collar for retaining the pin, makes them pretty chubby. For a 3/8 impact universal joint, I would opt for a Craftsman branded pinless version. they're relatively slender but, you'll need to shop around for a decent deal.
Speaking of deals, don't buy anything from NAPA unless it's on sale in their real deals flyer. NAPA can be pricey without a commercial account or not on sale.
lastly, if you were asking about impact swivel sockets, Sunex, Grey Pneumatic, NAPA, or Gearwrench versions will serve you well without breaking the bank.
