The primo has many incremental improvements over the Burly with only a minor increase in the cost to build. Its increase in stiffness will make it a bit better for aluminum. Judging from forum posts, aluminum is on the outer edge of the capabilities of the MPCNC. Some get it working, other struggle. The size (particularly the Z height) play a big role in the success of milling aluminum. Going forward you will find more support for the Primo. There is a longer answer concerning Primo vs Burly in this forum topic.