We have a set of those aluminum jack stands. They are flimsy looking and I would only use them for stabilizing, not for supporting a heavy load.
They do NOT have a safety standard rating that would be ANSI/ASME PALD-2009. The manufacturer can put whatever rating on them they want, but without a safety standard listing/rating they should be considered unsafe for other than stabilizing. Definitely do not support a vehicle or RV and work underneath one using these stands.
Also, jack stands are rated in pairs (by ANSI/ASME) so a 3K lb rating for example would be for two stands.
