These bikes look pretty refined. The only real direct competitor to the Zero bikes is the Hurricane, and it is offroad only.
Hurricane 3.0 kW $7700
- 84 lbs
- 3 kW peak power
- 1.5 kWh battery (nominal?)
- 30-35 mile range*
- top speed 32 mph
Hurricane 4.5 kW $9900
- 105 lbs
- 4.5 kW peak power
- 1.5 kWh battery (nominal?)
- 30-35 mile range*
- top speed 50 mph
* very low speeds
2006 Electricross Drift $9250
PDF review- 140 lbs
- 14.4 kW peak power
- 1.8 kWh battery (nominal IIRC)
- top speed 44 mph (gearing limited)
Electricross evolved into Zero. Let's compare against Zero's latest off-road bike:
2013 Zero MX 2.8 $9495
- 223 lbs
- 20 kW peak
- 2.5 kWh battery (nominal)
- 35 mile range (FX 2.8 city)
- top speed 85 mph
I don't think there's a whole lot of overlap, honestly. Every year Zero moves farther away from their super-MTB roots, and Stealth is continuing to refine the super-MTB design. There are certainly trails where even a 105 lb bike is too heavy, and Stealth offers something in that market. Zero does not.
But then.. if weight is not an absolute gating factor, the Zero MX is a hugely more capable machine. Just depends on what your expectations are.
When Brammo ships product, they will be a direct competitor to Zero. Stealth really is not.