It would be nice to just select it from the GUI what CSS framework you want to use. In my case bootstrap just works better for me in a way that it is just easier for me to code in (and what I can see a little more support / plugins on the internet).
The other thing is that the current included foundation framework is the old version and not the newest version of the framework. You can easily fix it yourself however kinda annoying when browsing the docs that you need to select an older version.
(The switch inside foundation is a good example where the new version of the framework has a nice extra option the specify text inside the switch where the old version has not).
The COTG components are almost one one compatible between foundation and bootstrap. (You only need to change some classes and move around with the tag).
And you are right I am fully coding the form outside the designer and after the design process I just copy everything inside the body to COTG.