real world- the uc300 eth is a superb controller. i would definately spend the extra and get ethernet version.
i have 3 machines running with it. (and 3 previous customers retrofits running it too) much better using the uccnc software too . its very similar to mach3 to use but without its flaws.
i have just ordered another 2 full systems for next machines to be retrofitted over xmas break.