Just to bad that the CSS mode do not work versy well for justified galleries
That, really, is a matter of opinion. At the end of the day, you get used to seeing things in a certain way (and, more importantly, what you are getting is a justified grid even with CSS – just a different number of images in the rows). And as I have said, the JS mode doesn’t guarantee that things will look the same every time. Because of the random number of items per row, it is very much possible for the last row to have 1 item. E.g. for a long time in the JS mode itself, the demo page for Flickr on my site used to have one giant image in the last row. While it doesn’t look that great, you get used to it being that way, and on a mobile device it does not make much of a difference. In fact there are some users who prefer having huge images on their landing pages.
One thing you can probably try is to reduce the value in Photonic → Settings → Generic Options → Layouts → Random Justified Gallery – Minimum Tile height. There is a chance that might fit more images in the same row even in the CSS layout.