The Alphatron LCD is 960x480. So is half the width of the 1080p signal coming from the SDI. That is pretty high resolution for an EVF.
As a point of reference its the same resolution as the LCD EVF on the Sony F55. The OLED EVF for the F55 is 720p. The Zacuto is only 800x480...
The Alphatron just scales the HDSDI signal. Not sure where you read it cuts the signal?? The Alphatron, like many others, offers various scaling modes including 1to1 pixel mode (available for critical focus) so it's not cutting the signal.
As for monitors... Very few field monitors run HD resolutions. Most are less than 720p. Most just scale the HDSDI signal.
FYI I own the Zacuto and am happy to discover that the audio meters work really well on it. Actually getting pretty good sound from a Rode VideoMicPro, as well as a Sennheiser ME66. I've been connected from a Shuttle2 but am switching to a SDI to HDMI converter shortly for a smaller footprint.