I've worked for a few companies that "require" us to use concur. I'm not fan. I'm sure there are worse products though.
Much of the issues I have with Concur is related to the back end expense assignments. Most of the major problems with Concur come from your own corporate accounting settings I think.
A couple tips on things I've learned over that past 15 years using this system.
If you want to book a certain flight on a certain carrier my suggestion is the work the flight backward. Go on that airlines website and find the flight you want. For example say I want to fly on AA from DFW to ORD on the 9am flight. I don't want the 6am flight. When you go into Concur set the flight time tight so you need to leave at 9am +/- 1 hour or whatever. Then do the search. It might come up with some alternatives but the tighter and more limited you make the search the better your results will be.
Second tip is once you book the flight, don't, repeat...DO NOT...pick your airline seats through Concur. It will screw you up more than it will help you. I've done this, picked seats on Concur, then gotten an upgrade or MCE seat only to have Concur override it and pull me back to the original seat selected. Just don't do it.
The best blog post on this issue I've found is at:
http://www.travelcodex.com/2015/01/h...travel-concur/