The real benefit is from the website though and not the transmitter. I was hoping there was an option of using the comparative features of the website (even if for a fee) without having to buy their transmitter but that seems to not be the case.
For a true comparison of antennas one would either need two WSPRlites or the patience to switch between the two antennas multiple times at various times of the day and night. Otherwise, some differences would have to be attributed to changes in propagation.
The one benefit for those not wanting to buy a WSPRlite is that band openings and closings can be easily seen by running your own WSPR set-up for a day or more and then looking at the "DX10" graph generated on the free portion of the website.