I dual builded my Fortunata/Widow where I find the dual build to be the most use for my team and I.
I do wish there was an option to just use the same enhancements is you are picking the same powers. To refit all the enhancements bankrupt me and it seemed silly that I was refitting certain powers with duplicates of the exact same enhancements for the exact same powers in both builds seemed to serve no purpose. If a superhero has power a in one build and power a in the second build, why would he need to switch out complete enhancements. Its like telling a comic book hero "sorry but your cybernetic heart doesn't work in this configuration, so we'll need to do surgery each time just to give you a new power when you change suits."
Also, the 15 minute timer AND having to go talk to a trainer seems to discourage dual building and its usefullness to teams. A simple fix would be to all switching on the fly, shorten the timer to 5 minutes, and put in something that says you can't switch builds inside a mission area.
Also, when leveling up, leveling both builds is frustrating, as is using enhancements. There is currently no way that I can be on build 1, and then stick a dropped enhancement into build 2, or level build 2 without being stuck using build 2 for 15 minutes. A button allowing me to enhance both builds without switching builds, and a way to level both builds without being forced to be stuck on a build for 15 minutes would help remove the frustration of the 15 minutes timer.
This is especially true if I find that build 2 is more useful to my current team, but level and have a tray full of enhancements or recipies I can use for build 1, but am afraid to switch over to build 1 because of its lesser usefullness to the current team, causing me to either have to travel to a vault, have some things full preventing me from getting drops, or sell things I can use to free up room.