I have run one of these units all year long, and love what it does for me. You’ll wanna check this link.
http://www.idofishing.com/forum/showflat.php/Number/1117131/fpart/1/lowrance-elite-5-dsi-screen-shots
These are screen shots that I took with my camera. As the year progressed, I was able to read it better all the time. I use it in conjunction with my Lowrance 510. So when I have a question about what something is on my regular sonar that I’ve been used to for a while, I just look at the DSI and can usually see it’s a tree, grass, baitfish, or whatever. The two units’ interference with each other is very minimal, so it’s become a valuable tool in my boat.
It does no mapping. I believe there may be a unit that has mapping capabilities, but mine is not that unit. I have another unit I use for mapping only.
Of course the price point is very attractive on the unit, partly why I bought it. I picked it up for only $350 at the time. As mentioned, it doesn’t really compare to the Structure Scan Lowrance offers, but then again, the price doesn’t either. It serves a specific function in that it looks straight down to help you find structure and answer questions. The side imaging is a different ball game and personally I think it has some distinct advantages when looking for fish in certain situations. But save your $$ for one, that’s for sure.
Hope this answers some questions. Let me know if I can help further.