This is a really good question.

LoungePair lets you name your own price for access to airport lounges.

LoungeBuddy on the other hand acts as a conduit for airport lounges to sell access, typically at full price.

While our pricing model is likely to make access more affordable if the lounge accepts your offer, it doesn't come with the same access guarantee as receive when you purchase lounge access at full price. 

Further, LoungeBuddy has been acquired by American Express. As a result of the acquisition, lounge booking services are exclusively available for American Express Card Members only.

You can no longer use LoungeBuddy if you have a Visa, Mastercard or Diners Club.