Welcome to AA
I share your concern with that deal!
I agree with all of the above, drain it, and if you see that the stand itself is wobbly or weak in ANY way I would make a beeline for the store and return it.
It benefits the hobbyist community when you show your vote against underbuilt fish stands. That is a serious issue and you have about 500lbs of stuff on that stand with the glass, water and gravel. If it fell over it could really injure someone or worse as you said.
You could get a nice heavy wood stand with a big base on it and you'll sleep a heck of a lot better knowing that when the kids accidentally crash into it when they are playing, that they are safe from harm. Also, a wood stand will distribute the load much better across the joists, and not have up to 125lbs per square inch of load pressure like the feet on your current stand have.
Let us know how it turns out, we will be interested to hear of your solution and also to help out with any further aquarium issues!