QZone has adjustable legs so you can use sitting or standing. Carriage has rails for dual track wheels. Other than that they appear to be pretty much the same. I have had mine since 2016 and with a few minor fixes it has served me well. If you get the SR2 the carriage will most likely have a single wheel track. If you are using a domestic machine that won’t make a difference to you. I needed a new ratchet wheel and discovered the SR2 and QZone used the same one, it sure looks like the rest of the frame is the same also. If you get the SR2 let me know and I can tell you a few cheap easy fixes to make it easier to use.