For Saver Level business class awards buying miles can be an excellent deal. Although those awards are rare in normal times they have been more frequent since Covid hit. So if you have an immediate J Class Saver Level award available I would go for it but otherwise I would not buy miles as the opportunity to extract good value is few and far between. You have to get very lucky to find something that works for you. Cash is King as they say.

An example of when it can work out. I had a couple of family members that needed one way tickets from the UK to the US a few months back and they were able to get business class for 57,500 miles equating to just over $1,000 each after they bought the miles. That was almost the same cost as the cheapest coach fare they could get (which required buying a return and throwing away the return segment). Business class tickets were selling for nearly $6,000. In normal times they would have been unlikely to find 1 Saver Level award, let alone 2.