As a Systems Engineer, I'm not sure everyone fully appreciates the difference and value of the “Flat High Performance” (AKA Flat HP) dish i.e. the $2,500 hardware system. The Flat HP is larger, 22.6" (575 mm) x 20.1" (511 mm) vs the older 15.7" (400 mm) x 11.8" (300 mm). The Flat HP also has a wider field of view – 140 degrees vs 100 degrees and a better GPS chip that allows more precise satellite tracking. The most overlooked feature is that the Flat HP actively tracks satellites even in motion, allowing the dish to compensate for platform pitch and roll motion, which is the primary reason for the wider field of view (to compensate for pitch and roll). For the SL antenna to actively track satellites, each antenna element in the phased array must determine the phase difference between the received signal to determine the difference between the line of sight (LOS) to the satellite and the mathematical LOS to the Satellite's spatial location assuming a horizontal platform. This allows the SL system to determine the real-time platform pitch and roll angles and to correct the pointing angle of the transmit (Tx) beam. The difference in the complexity of the Flat HP and the older non-mobile antenna can not be overstated. The difference in processing requirements and software complexity accounts for the difference in cost.
So, what is the value of the Flat HP antenna? When tied to the dock in a calm harbor, or anchored in a protected area I would expect a moderately higher data rate, but at sea in rough conditions when you're rolling the old fixed antenna will be "obstructed" beyond some roll angle because the satellite won't be where the antenna thinks it should be. You'll still get some data when you're close to horizontal, so I think it won't drop to zero. The Flat HP system is supposed to maintain the service (I'm guessing it would have a small performance degradation because perfection is unaffordable).
If you only want or need data in calm conditions while stationary (although you might get service while moving slowly, that isn't guaranteed to continue indefinitely), then the older smaller antenna should suffice. If you want data while underway regardless of conditions, then you should get the Flat HP antenna.
