Not intentional, but it looks like I have a bunch of them.
Here is what I got
HDHR-US 101xxxxx is gen 1/2
1012xxxx or lower is gen 1
1013xxxx or higher is gen 2
HDHR-T1-US 102xxxxx is a single tuner version of gen 2
HDHR3-US 103xxxxx is gen 3
HDHR4-2US 104xxxxx is gen 4 (CONNECT)
105xxxxx is the transcoding model (EXTEND). Early production runs had gen 4 tuners, later ones had gen 5 tuners. There’s a plastic version with a fan, and an all-metal version that is a passive heat sink.
HDHR5-2US 106xxxxx is gen 5 2-tuner/DUO
HDHR5-4US 107xxxxx is gen 5 4-tuner/QUATRO.
HDFX-2US 109xxxxx is basically the DUO (106) with a USB port exposed for the HDHomeRun DVR service
Weight: 332.2