The Cudy routers WR3000E (R53) and WR3000S (R59) share the same hardware (mainboard) besides the case (and therefore the LEDs) and the antennae. WR3000E follows the design from the "old" WR3000 with the 6 LEDs. The WR3000S has the newer design with 10 LEDs. The software seems to be a bit different: if you compare the firmware files (e.g. v2.27): it seems to be the case that it's mostly different because of the LED-functions, different model number and, of course, the hash value.
Why they haven't released an intermediary OpenWRT-firmware (yet?) is beyond me. Maybe they want to justify the higher price for the S-model? There usually is a 10 to 15 Euro difference between these models. It's not unusual for manufacturers to saturate different market (price) segments with the identical hardware to reach more customers without making it too obvious that a part of them is paying more for the same hardware.