I have limited experience with alu. sp.gun welding but do own a nice miller gun, and bought a nice XMT 350 to power it. Back in the early 80s I worked for a small tea kettle to catapillar repair/welding shop, great experience/low pay,moved on after 3 years.
Spent some time with the spoolgun in a few aluminum dump trailers, 1/4-1/2" thick stuff, could make some nice welds. 1/8" and down, not so much, so I rather use my tig system. Thinner the harder. I found that a larger .035 wire tends to work better than .024 on thinner material, wire speed is key. If you have scrap the same as your welding,"a must" and can control the gun with 1 hand and one on the wire speed while welding is the best way to set the system.