Having not delved too deep into attempting VNs in Japanese, I've only used the anime difficulty features, but I've found it to be useful for narrowing things down. In particular I first search for something I'm interested in, and if it's above a Difficulty 3 I sigh and pass it by =P
just commenting to say that jpdb is an amazing srs utility too, the difficulty lists are great but they should really be used in conjunction with the rest of the sites features