I went to BPS yesterday to inquire about these units. I was told that the one with the internal unit was good enough for my boat, although I did not think to ask about mounting it into the dash. The salesman told me that a lot of the pros use it but they tend to use it laying flat and the unit would loose its signal. He said as long as it was mounted in the bracket it would work just fine. I asked about the hummingbird units with GPS and they use a mapping system which just shows the contour lines where the lowrance unit uses a mapping system that shows the old river bed and bldgs and such. I do know that lowrance is coming out with a new model for next year and the older ones should be going on sale to make room for the new ones. The map disk cost about 100 dollars for each region. I hope this helps you out on your question. I am still debating on when to buy one for myself. My wife agreed to get it for me so I may have to hurry before I do something to make her mad and have to wait until next year.