500 Mbps or 600 Mbps?
You'll notice the "500" in Linksys' product name, which alludes to the "Technology: Homeplug AV2 500 Mbps" in its specification. ZyXEL, on the other hand, quotes a 600 Mbps transmit/receive data transfer rate in the PLA5205's spec. If both are based on AV2, why the difference?
First, to recap, remember that "500 Mbps" HomePlug AV—which is not an official HomePlug spec—gets its extra throughput by using a wider frequency spectrum (2 to 68 MHz) than the 2 to 30 MHz spectrum that standard (200 Mbps) HomePlug AV uses.
HomePlug AV Frequency Use
According to this diagram from the HomePlug Alliance, AV2 expands the spectrum even more, out to 86 MHz. Note also that there are two forms of AV2—SISO (Single Input Single Output) and MIMO (Multiple Input Multiple Output). Homeplug AV2 uses a lot of the technology used in 802.11n and ac wireless, including OFDM, MIMO and even beamforming!
HomePlug AV2 Attributes
I reached out to ZyXEL and Qualcomm Atheros for an explanation of ZyXEL's 600 Mbps claim. Q-A sent the diagram below, which reveals two SISO and three MIMO bandwidth profiles. But note that Q-A supports only the SISO-500 profile in its current chipset, which is used in both products.
Qualcomm Atheros Supported HomePlug AV2 Profiles
In its email, however, Q-A offered this additional information:
However, our silicon is capable of delivering up to 600 Mbps if the HW design has the lowest noise profile. So, customers who are able to do a good design can realize the 600 Mbps rates. So we can call ourselves SISO-500+.
ZyXEL apparently thought "600 Mbps" sounded better than SISO-500+ and went for it. And since ZyXEL's adapters are not HomePlug Certified, I guess they can claim what they want. Note that Linksys' adapter is HomePlug Certified, but only against AV, not AV2.
The adapters were both easy to open, although the Linksys required a bit more prying once the single screw covered by its rear label was peeled away. The designs are so similar that I thought it best to show the boards side-by-side in the photo below.
Linksys PLE500 and ZyXEL PLA5205 inside
The large device is a QCA7450 with the much smaller AR1540 analog front end sitting to its upper right. That's an Atheros AR8035-A single-port 10/100/1000 Ethernet PHY sitting right next to the Ethernet connector.
While the boards are not identical, I imagine they don't deviate very far from Qualcomm Atheros' reference design.
Like HomePlug AV, AV2 devices are protected with 128 bit AES encryption and come set with the same default key, so you can just plug and play.
All AV2 devices have buttons that can be used to change the security code. Setting the code works like setting up a Wi-Fi WPS connection. You press the button on one device until a LED starts blinking. You then have two minutes to press the button on a second adapter to complete the setting.
The ZyXEL came with a utility on a CD. Linksys also supplied a CD, but it contained only documentation. You can, however, download its utility (Windows or MacOS), which is shown below. Both utilities rely on WinPCap, which they will automatically install if your system doesn't already have it.
Linksys PLE500 utility
Both utilities detected each other's adapters and provided the same features. They differ mainly in presentation format. So if you don't like the utility that came with your adapter, hit the product support page for the other product, download and install its utility and enjoy!
I used the ZyXEL utility to grab the firmware version for both products. The PLE500's info is shown below, so that you can compare to the Linksys utility's presenatation of the same information above.
Linksys PLE500 Firmware version
Comparing with the ZyXEL's firmware version shown below shows the Linksys uses a slightly later version.