I use responsive lightbox in my theme “vantage”. I have two issues:
1. When I use other than the default theme in the lightbox settings, then I have nasty frames around my large pics, more or less large and faulty depending on the padding I set in the lightbox settings. With the default setting it is usable, otherwise it’s ugly.
2. The so called “responsive” display of the large pics on a iphone is not usable. It’s definitely either way too small displaying or not at all displaying. (…difficult to explain without showing a pic of the display)