I updated the topic you linked to. Here is what I added:
The sampling rate, the hardware platform and the firmware is the same for the EyeX Controller and the Steelseries Sentry eye trackers. With the latest firmware I believe it averages around 60 Hz when the tracking is good (few lost data points).
You can use the Steelseries Sentry just as well as the EyeX Controller for developing with the EyeX SDK, there is no difference from the EyeX Engine’s perspective.
The difference between the two is that the Steelseries Sentry is branded and comes with a software for gaze-overlay in streaming and an analyzer tool to help players enhance their gameplay.