I own and use two Tablos, both a 4 tuner and 2 tuner model, with identical disk drives, antennas, and very similar ambient confitions.
The 4 tuner Tablo is definitely more flakey. I have missing recordings, partial recordings, fragmented recordings (an episode shows up as 2 separate pieces) whereas the 2 tuner unit very rarely misbehaves. If I REALLY want to ensure a recording of a special show I have learned to record it on BOTH Tablos.
For those with light recording schedules, I would suggest that the 2 tuner model is a safer choice.