Since I have never cast a combo fly rod so I probably shouldn't even post on this. But I will anyway
. I lump combo fly rods in the same catagory as spin / fly rod combos. They might work for two different situations, but may not do either great.
Personal opinion: Buy the right rod(s) for your various fishing situations. Just like a golfer doesn't carry one club for the entire course, the same rod doesn't work for all your given situations. Yes, the initial cost of a couple of rods will cost you, but I am betting you will end up buying more than one rod/ combo. Then again I am a certified rod junkie and build my own
All we can do is speculate on what your preferences are. Cast as many rods as you can.