re: The MERs are pretty much at the outer limits of the technology
But it DID work!
People can argue that, if the skin of the LEMs were any thinner, it might have not sustained vacuum/shirt sleeve pressure differentials, but it worked.
If we started fretting about every little bit of data that came close to our interpreted extrema of their expected performance, we'd never get anywhere- namely, the moon, or even Mars.
If the MERs crashed, no lives would have been lost- it's just money. Isn't that the best time to take the risk?