It has the same number of buttons as the 525 and features colored buttons typical on most satellite boxes. It has a four-button, monochrome LCD display. This remote is software limited to controlling up to five devices. Like its mid-range cousins, the 520 and 550, it has no recharge pod and uses AAA batteries instead. Unlike previous 500 series models, these newer models have been limited to 5 devices in software, yet sell for the same prices. Difference between 510/515: The 510 is black; the 515 is silver. The Harmony 520 is a mid-range remote that is similar in functionality to the Harmony 659 and 670, but with a different button arrangement and a squared-off physical design compared to the hourglass design of the 6xx series. It has a blue back-light and monochrome LCD screen. These 5xx models are equipped with an infrared learning port to learn IR signals of unsupported or unknown devices. By pointing an original remote control at the Harmony's learning port, it is able to copy and reproduce those codes and, in the case of supported devices, it is able to figure out what the remote is used to control and imports that device. They require 4 AAA batteries. A mini USB port is used to connect these to a computer for programming. Difference between 520/525: The 525 has 50 buttons, while the 520 has 46. It lacks the red, green, yellow and blue colour buttons commonly used for things like teletext and PVR control. Apparently, the 520 is the American model while the 525 is the European. The 520 and 525 can control up to 12 and 15 devices respectively. The harmony 550/555 remotes are variants of the 525 remote. Compared to the model 525, the 550 and 555 have two extra buttons, and are made of higher grade materials with different colors. The 550 and 555 models both have a sound and a picture button that changes the button mapping on the remote, allowing for reuse of the same physical buttons for different set of functionality. 52 buttons. Difference between 550/555: The 550 and 555 have the same number and placement of buttons, just with different mapping. The 555 have the same color buttons as the 525. The 550 does not, instead it has the following extra functions: Up arrow, Down arrow, A and B buttons. The 555 has orange back-light, the 550 has blue. The Harman/Kardon TC 30 appears to be a redesigned, rebranded Harmony 52x with a cradle and a color LCD.