Does the flat mount perform the same as a normal dishy?

Performance will depend on many factors. Short said the dish no longer needs to move, as proven by the new versions (flat high performance and v3). Here are the factors that we consider most important for speeds:

• The flat mount should be relatively even. Setting it up at an angle is possible, but it might be pointing away from satellites. Having it flat and even will make sure it works in almost all cases. (A 2-3 degree angle is no problem and is recommended to support the water running off your flat mount)
  
  
• Make sure that the sky is visible. Trees are the most common reason you are not getting full speeds and interruptions. Starlink's documentation is specific: "Each Starlink should have a clear view of the sky 20° elevation above the horizon, 360° around the azimuth. You may need to raise the antennas on a pole/pedestal to get a clear view of the sky & good service. If you have obstructions > 20° elevation in any direction, the connection may be occasionally interrupted."

The speeds to expect with a flat mount are usually slightly less than with a normal dish. We typically see around 100 mbit download and 20 mbit upload with a flat-mounted dishy and completely unobstructed sky.