Just be aware the benefit of using the 2 ohm switch, especially with a single One 10 cab, is that it limits the maximum power output to about 300 watts or thereabouts. This was actually suggested by the designer of the amp in the Mesa subway thread. It provides an additional level of security that you will not blow the speaker, and without any audible change in tone. It is still more than enough power for a One 10, and is the setting I have always used with my One 10. Of course, you can simply leave the amp switched to 4/8 ohms and rely on your ears to avoid speaker overload, this is what I do with my Two 10. Be aware that Alex suggested it is easier to tell when a twelve speaker is being pushed too far than a ten, since the tens have a baked in tone which might disguise it whereas the twelve is as close to neutral as I have ever heard.