Has anyone used these things. I was looking on getting one for my small electric powered boat so I would be able to see depth and bottom contour. I'm not sure how well these would work for an actual fish finder because the articles I read say it only has a 6 degree cone which is pretty small.

Any comments are very welcome

I have the fishin' Bubby 4200. It has a 18 degree cone. It is a great little fish finder. It has all the features of a fixed unit in a easy to use portable format. I use the same way you intend to use it. With the 320x320 screen you will have more detail than the lower priced fixed units. It shows fish very well.

http://www.bottomlinefishfinders.com/site/html/htmlsite/bl/4200.htm

With the 18 degree cone in shallow water you wouldn't see to much, I would think.

with an 18 degree cone you will see about 1/3 of the depth in a diameter of the bottom. For example in 30' of water you will see a 10' diameter circle at the bottom. You will find most fish finders have a 20 degree cone and those with dual cones will have 20 and 60 degree cones.  

Other than the 320x320 screen the other reason I got the 4200 is the 18 degree cone. The other models have a 9 degree cone.

The only issue I very had was as you increased your trolling motor speed, the thing starts to rock back and forth. Had to take it out of the harness......not a huge issue but irritating.

Here's another option.

http://www.basspro.com/webapp/wcs/stores/servlet/Product_10151_-1_10001_75236_200001001_200000000_200001000_200-1-1