I have the Lowrance X50DS fitted to my Swing which I bought from BCF at Labrador for $260 (haggled) back in July this year.
I had a few problems getting the transducer to work but it seems to have sorted itself now. Could be the goop I used initially (Selley's aquarium silicone) but ended up going with Sikaflex. The transducer is not a flat puck shape but rather a skimmer type designed for less bubbles when fitted to the back of a stinkboat.
Have yet to see any definitive fish arches like those shown on the simulation mode.
Also I'm wondering about the use of the dual frequency... The manual suggested that the higher frequency 200kHz was more suitable for shallow water which is where I do most of my fishing. In the end I think it's a bit gimmiky.
For what's it's worth here's the link
The X52 is probably a better unit in my opinion but probably hard to justify the extra $$$.
On the plus side the X50DS is easy to use and quite a neat unit with a small mounting footprint The X52 has quite a long wide base (Sel used to own the X52).
In my opinion you're probably better off getting a higher model Eagle which are essentially made by Lowrance anyway (similar to what Dodge has)
Important part is to tell depth and contour.. I don't think you will see accurate fish symbols unless you pay the $$$.