Thank you all for this useful info.
We can't have the contacts weld together and then the breaker not open when it needs to. I do some welding and can confirm that the AC and DC arc characteristics are quite different.
That fellow that asked me about the Home Depot breakers ended up buying a 8-to-1 combiner box for his PV array, with 8 Midnite Solar 15ADC 150VDC din rail DC breakers. He paid $10.70 for each breaker - not all that much.
I wonder what kind of technology they use in these DC breakers to overcome the DC arc problems, surely cannot be as expensive as some of the methods described above. Maybe thicker contacts, different contacts shape, contacts plating, some simple arc suppression techniques, ..., does anyone know, or ever disected a DC breaker?