Mixed Fleet Flying- pro's and con's?
 

Since at least 30 years or so airplane manufacturers had been strongly advertising cockpit commonality and ability to fly different models of their products by the same group of pilots- it had been a big selling poit.

Meanwhile, most airlines seem to be reclutant in implementing MFF, especially between smaller and larger models (eg. A320/A330, or 737NG/787).

What are the pro's and con's of doing so? The ones I can think of:

Pro's
- better flexibility for crewing
- more variety for pilots
- more landings for the longhaul guys, more practice

Con's
- perhaps the differences between models are more pronounced than OEMs tell us?
- difficulty in efficient crew planning of SH/LH ops (rest periods etc.)
- seniority issues (senior guys don't want to get dirty' flying multiple sector SH)

Can anyone with experience of MFF comment/add something to this list? Which operators use MFF?