I've used both Boroda and PRS+. I don't believe you need them both as they offer the same font customisation options. The only difference (I think) is the directories where the various system files are stored. Both offer the ability to customise EPUB fonts and RTF/TXT/LRF fonts via 2 separate options.
However, I don't know whether Boroda offers other features which are desirable for Russian readers. I only read English I'm afraid, so I can't comment.
If you have 2 different types of EPUB you want to read (Western and Russian) the logical thing to do is to have 2 separate CSS files on the PRS650. One for Western books (LexiaDaMa font) and one for Russian books (??? font). PRS+ will let you switch between CSS files as needed. I can't remember whether Boroda offers the same switching feature.
You can also use CSS files on the PRS650 to adjust font-size to your liking to get round the poor zoom features on the Sony (ie differences between Small/Medium/Large too great).
Last edited by jackie_w; 07-27-2011 at 04:06 PM.