[j-nsp] Reliability of M20 chassis ?

[joe mcguckin]

I notice that Juniper came out with the M20e chassis which can accept a
redundant route engine and switch fabric board.

Has this been a real problem that required a fix? Or is this a feature that
rarely is used, but makes owners feel more secure?

There must still be a lot of original M40's out there. Are they running ok
or are carriers replacing them with M40e's ?

Thanks,

Joe