Interesting question. I guess the answer depends on what you're planning for, and what results you expect. In particular: reliability.

I've noticed quite a lot of these mish-mash units for a very attractive price.

If you're, say, a tradesman doing work in a new housing development, these are great. They will probably work out of the box and keep your tools rocking. You will drive them until they die. And if they fail, you take them back. No problem.

But if you're planning for unpredictable power outages due to blizzard or heat wave or major storm, where keeping the heat/cooling on, and the water pumping, and the fridges and freezers from trashing half a side of beef, not to mention cooling somebody's life-saving med's, you may prefer a unit where somebody has signed off on the engineering.

My 2c.