Thanks for your suggestions but I can't quite get the layout as I want - or not in a very satisfactory way. Basically, I would like to know which P7 extension would be most suitable for a responsive grid of images wrapping with this result: http://bit.ly/images_samesize, rather than this: http://bit.ly/images_differentsize .
The layout, using FGM is as I want here, except for the problem of the final image: http://bit.ly/fgm_1 . Here - http://bit.ly/fgm_2 - I've given each image the same width basis, as you suggested. This didn't seem to help, though I didn't set grow to zero (as I want the images to grow, as long as they're the same relative size). This is also an example of the issue I asked about in my earlier post - about controlling the layout/wrapping in FGM; these two layouts are quite different but I mainly arrived at the one I wanted using trial and error.
Using jQuery, I can get the desired result, but it's not completely reliable: http://bit.ly/fgm_jq. I can also get the right result using Bootstrap, but I would rather not use Bootstrap: http://bit.ly/bootstrap_1.
I think you're final comment is probably the key - not to use Flexbox, though FGM does almost exactly what I want except for this one detail. Using a non-Flex grid system (like Bootstrap) is one answer. I tried with LBM, but this isn't responsive in the same way: it's either 4 images across or just one: http://bit.ly/lbm_1. If there were more media query break points it would work; I don't know how feasible it would be to add a new class for this, to extend what LBM does.
Is there a P7 product you would suggest or can you suggests tweaks to any of the above? The thumbnail displays of Magic Box might work - but obviously that's not the point of MBX. The images will not link to larger images but will run database queries and display search results relating to different categories.
I'm sorry for a rather long post but I expect there is a good solution among your extensions which I could see if I were more familiar with them. There are quite a few situations I would find FGM useful, but for these purposes it wouldn't make sense to have the images other than the same relative size. I would be grateful for any suggestions.