I just got done fixing one of those for a neighbor of mine, he's over 400 lbs and bought the bike about four years ago on sale cheap against all warnings.
The bike itself isn't bad but its got a few weak points. The latest with my neighbor's bike was the front axle, he said he it gave way while jumping the driveway curb into a McDonald's last Friday.
The rear hub looked good, and the week wasn't damaged other wise. The bearings and axle could have been easily replaced with a common Wald axle kit but knowing how he treats the bike, I figured something heavier was in order. I dug around and found a good 10mm axle, then I knocked out the front cups, found two bearings to fit with a 10mm ID and appropriate width. I measured and cut a center spacer and two outer spacers and found two washers. It now has a sealed front hub with a 10mm axle vs. the 5/16" axle it came with.
He also had to upgrade the handle bars, both bent under his weight, but he was likely riding off curbs or such. His original tires are long gone, they didn't last him but a few months.
I mount his tires using cotton rim tape, tire puncture proof strips, and thorn resistant tubes filled with Slime. The tires are what ever cheap 700x28 tires he finds. He went up in tire size because they fit and they were cheaper. (Weight isn't a concern for a guy over 400 lbs. He broke two freewheels, the first one rusted seized, the second one was an eBay special that he stripped out in a month. Its now got an old school BMX freewheel from the 70's on it. The original pedals also died early, but he found a set of bright purple BMX pedals for his that solved that issue.
The new handle bar is a straight aluminum mountain bike bar.
The rims themselves have been fine, he lost a few spokes on it here and there but mostly from branches and his big feet. He bought a huge old Cloud 9 saddle at a yard sale, the original seat was fine but he couldn't ride on it.
The BB, cranks, and rear hub have all been fine. Most of the issues, like I said were from abuse or his size. It is built pretty heavy, the welds look decent and the tubing is huge so I doubt the frame will die of anything other than eventual rust from his keeping it behind his bushes in the yard and not in a garage or out of the rain.
Its lasted him by far longer than anything else he's come up with over the past few years, but he's the type of guy who could break a crowbar in a sandbox if you know what I mean.
One good example of how he rides is that he don't use the brakes, he'd rather use his boots, he jams his boot behind the front wheel to stop, he says its faster than pulling the levers and that way he can keep his phone or beer in hand while he rides.
I do agree, these bikes are perfect for bigger guys, they built the frame like a tank and the 48 spokes make it pretty tough to kill the wheels. If ridden like a normal bike should be ridden, you likely won't have any issues with it.
I find a lot of the issues with the box store bikes is set up, they leave the assembly to some 18 year old kid who don't know a bike from a beach ball and turn out the bike good or bad to the buyer. Most buyers of that kind of bike are the worst person to own one because many or most have no ability to correct minor issues before they become major ones. The bike to them is either good or bad, good means it rides fine, bad means something fell off or doesn't fit right because it was assembled with a monkey wrench and hammer.