Based on the Sovol3D online store, I’d say the difference between the Zero tool head and the SV08 Max tool head is $30. 
The SV08 tool head looks taller so maybe an even longer melt zone?
From the specs, both hot ends have a 50 mm^3/s flow rate, but the Zero has a maximum nozzle temperature of 350 C and (ignoring earlier website misinformation) the SV08 Max has a maximum nozzle temperature of 300 C. Both printers use MK8 nozzles.