Thinking of joining the club need advice.

As "The Critic" rightly pointed out, it could work out cheaper in the long run, even if you just threw those tires away. Those tires could be costing you more 10% in FE and well more than $500 over the life of the tires.

In my opinion it's silly to use non-LRR tires on a Prius.

 

Of course, it's also possible that he removed the good LRR tires for his own use and put cheap ones on.

As others have said, LRR tires pay for themselves in the long run. It's not just the mileage, but they're likely better quality tires. For high mileage many swear by Goodyear Assurance FuelMax: not a winter tire, but as long as you take care you can get through winter. And they have max sidewall of 51psi so you can comfortably inflate them to high pressures. You might be able to sell the Kendas to someone with low miles for whom cheap is best.