I also would love to see a head to head of these two, the specs look pretty close. The Alta has more torque while the FX has more horsepower. The Alta might be quicker off the line but tops out at 65. The Zero probably has a stronger midrange as it has peak power around 4300 rpm. The Zero single module is slightly lighter, but with reduced power, the dual module is heavier but also more power. The FX can do 85 mph. The other difference is battery, looks like the Alta is 5.8 kWh and the Zero is 6.5 kWh.
So the specs are relatively close, maybe a little edge on the Zero with the larger battery, more power, higher speed, and ability to ride on the street with lights and signals. You would think the Alta would cost just a little less or about the same, but its about $4500 more for some reason which also leans heavily towards the Zero. And the last thing would be experience and reliability. Zero has had millions of miles of real world customer feedback and failures to learn from that only expose themselves over time. The Redshift looks well built but only time will tell if it holds up as well.
However for strictly off road, at speeds under 65, and if money or maximum range isn't a consideration, and if reliability isn't a deal breaker if something goes wrong, there is no doubt the Redshift looks like it could be fun to ride too.
Hopefully one of the motorcycle magazines can do a head to head soon. I'd love to see their comparison and take on it.