You have to set it on high, and work with the wire speed that comes with. Some welds are pretty, some aren't. I'm getting good penetration and have a grinder, so it is what it is.
I hit my last set of welds with a sledge hammer about 30 minutes afterwards. None of them cracked.
We, and by we I mean my friends who taught me to pick up my skirt and start welding, welded the rack together with a much better welder that uses gas. The welder I have is good for small jobs and learning. Larger jobs, I'd suck it up for a few extra months and get a better welder, or go to my buddies shop and use his.