The 421E's inside photo shows the QCA7500 at lower left. That's an Atheros AR8035 Gigabit Ethernet PHY right above it. There is no separate analog front end (AFE) device; that function is built into the QCA7500. This board is plugged into another board below it that has the wall plug and mostly passive components.
TRENDnet TPL-421E inside
The 421E didn't get very hot during testing, despite its lack of heatsinks. The large ventilation slots on both sides of the device appear to keep it cool enough. It also helps that components aren't jammed into a tiny box. Here's a fuzzy view of the unplugged board underside showing 128 MB of Samsung K4B1G1646G RAM and 4 MB of Macronix MX25L3206E flash.
TRENDnet TPL-421E board bottom
TRENDnet includes a Power Packet Utility on the CD packed in the 421E2K's box. You can also download it from the product's support page. It requires WinPcap 4.1.3, which will also be installed if it isn't already. The screenshot below shows the Utility, which doesn't expose the incomprehensible QoS controls some other powerline utilities do.
The screenshot was taken with both adapters plugged into the same power strip, showing a 910 Mbps link rate. I was transferring a large sequential file when this screenshot was taken. Printing out the utility's report showed the identified the adapter firmware as MAC-QCA7500-220.127.116.112-05-20150511-CS.
Power Packet Utility
You can also use the utility to set the encryption key (aka password) if you don't want to use the pushbutton method.
I tested the TPL-421E using our standard powerline test procedure, with all results entered into the Powerline Performance Charts. I included two other top-ranked AV2-MIMO adapters, NETGEAR's PL1200 and TP-LINK's TL-PA8030P-KIT and the 421E's TPL-420E2K no-outlet sibling.
The Downlink Throughput plot below shows the TPL-421E having the highest throughput in the best-case same-outlet Location A, but in no other test location. Top throughput in Locations C and E was produced by TP-LINK's TL-PA8030P-KIT.
Downlink throughput comparison
Uplink results show the same relative performance results as downlink.
Uplink throughput comparison
The simultaneous up /downlink IxChariot plot for the TPL-421E at Location A shows higher average downlink throughput after an initial position swap. The 523 Mbps total throughput result was 17% higher than 446 Mbps Location A downlink result.
IxChariot simultaneous up / downlink
I'm showing the composite downlink IxChariot plot because the Location A trace was so flat and maximum throughput was an even 500 Mbps. I asked TRENDnet whether this was expected behavior and they said it was within the range of what they've seen.