Are there major stability differences between simple table legs and plain ones?
Given that your table is reasonably heavy (19kg), I'd choose the second leg ("plain"). (And for what it's worth, I can't come up with a good description of them either, except to call them steel box legs.)

The only thing I would want to do is attach a panel across the back of the two legs that would prevent the table from swaying left to right. If that's not clear, leave a comment and I'll include a sketch.

I'm less impressed by the standalone legs... for starters, the description seems to say that they can carry a maximum weight of 50kg. Somebody climbing on the desk could easily overweight that. The place where they attach doesn't seem very wide, so they aren't likely to take abuse.

Regarding leg length, you could fill up any gaps with felt pads.