I've used cheapoair in the past and it worked as designed (though I did not need to make any changes to the ticket, and honestly wouldn't expect to be able to do so).

I guess the biggest issue with consolidator fares is that there is no way for me to know for sure what the booking class will be (JustFly does seem to quote the actual booking class in the rules, not sure if it ends up being that though, cheapoair does not show one at all). If these fares end up not earning miles (esp. on UA MP) - that certainly would be one reason for a hefty discount. I wonder...