Adding this to the header to help anyone who comes seeking this information and can't find it - these adapters have an unpublished thermal ceiling of 45C and will throttle down to 10Mbps if it exceeds that. I cracked open the shell (use pliers to pinch the sides together and a small screwdriver to pop the faceplate panel off) and pulled out the internals, and found basically no thermal materials except for a copper sheath glued on. I removed the glue, applied thermal pads and small heatsinks and I've had no throttling issues since then. Dropped to 3 stars for the fact that this happens in a 70F well ventilated room with active cooling.
In my experience (I've tried nearly every adapter on the market), these Realtek-based adapters are least trouble out of the bunch. The price to performance ratio is unbeatable (twenty five bucks at time of writing) and they work great with my Netgear 10GbE switch (capable of 1/2.5/5/10). It'll saturate any spinning platter disk on the planet and give you USB-ish speeds for networked SSDs - I get about 275MB/s at best (theoretical maximum for this adapter spec is 312.5MB/s before network and usb overhead, so that seems just about right).
From personal experience, I can confirm the following as of March 2020 (using MacOS RTUNICv1.0.20 - Mojave driver):
* This adapter is capable of transferring at full 2500Mbps (verified with iperf3 and blackmagic disk speed test) on both Windows and MacOS systems.
* It does get hot and will throttle down if it overheats - I added a small thermal pad to dissipate the heat and that helps.
* Works fine through hubs without any performance loss (this is big for folks trying to integrate an existing single plug setup).
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