I usually use https://cpubenchmark.net to give an idea for relative computing power comparisons.
According to that the non-K is 5.7% worse than the K version which would be the difference of 56~57 vs. 60 frames for example and max power usage of 65W vs. 95W. Depends how much $50 is or will be worth to you, if it were me I'd go for the K, bc it will probably be worth it over the lifetime of the thing.
Be wary from AS-IS condition from now on, ask if it's not clear what any issues might be.