At least an external tuner can validate the antenna’s own performance independently of the Tablo (or any other DVR). Whenever I set up an antenna for a friend, neighbor, relative or acquaintance, I take my USB tuner and laptop with me to ascertain the maximum antenna performance right at the roof or attic. Whatever tuner is used below in the house, at least the antenna’s reception is verified at the source above and before any distribution of signal takes place throughout the home.
Typically I can compare how every tuner in my home behaves with respect to the measurements taken at the antenna and I can grade them. In most cases I can tell how a recording will turn out based on which tuner\DVR was recording a particular show based on these prior measurements. I know which DVR will give me the best pristine recording to archive in my library of shows. For example, I knew exactly what tuners would give me the best copy of the Downton finale to save. The best tuner (using these measurements) gave me an absolutely flawless recording (no pixelation or hiccup for two straight hours) as if the recording came straight off a Bluray.