I ran the Bottom Line unit for the last 2 years. JonN is right they have had a lot of problems. I had my unit in because of a malfuntion 2 times. The unit itself did do a pretty good job when it was working. It marks fish and bottom content very well.
Now that I have a new boat and need new electronics I can tell you that I will not be running a Bottom Line graph on my new boat. 2 times in 2 years is two to many times for me to have to go without electronoics.
Garmin was my unit of choice this year. I personaly have never heard anything negative about the Garmin units. I am looking forward to running Garmin on my new rig. For the price they are hard to beat!