As far as I remember you can only compare after you upload a benchmark test/suite result to the site. For example when you upload a VkMark benchmark your result should be shown on that test page under Recent Test Results. You can then select your result and some other to compare them. And if you select to re-run a test suite from Latest Test Results the text at the top gives you the command to run it and automatically compare the results, e.g. for GPU CPU HDD Usage and Temperature test Unigine Heaven Fullscreen 2560x1440:
Compare your own system(s) to this result file with the Phoronix Test Suite by running the command:
phoronix-test-suite benchmark 2410251-MRPI-241025885