I bought a humminbird SI/DI combo about a year ago. High dollar piece of equipment, but it absolutely has changed the way I fish. I've learned more about bass fishing in the past year than I have in a very long time (partly due to living on the water now like I've always wanted to).
Here's my advice after fishing with one for a year:
1. Get the biggest screen you can afford. I bought the 798 hd si. The neat thing about it is that it basically has all the technical functions of the bigger machines. However, the screen prevents me from seeing some of the detail I'd like to see, especially when I'm standing up casting. Trust me on this one...you will get addicted to using the thing and you'll understand why everybody has 2 big ones hanging off their rigs. I thought those guys were just posers!!! LOL
2. If you really want the full capability....it takes research and work to dial in your si and di settings as well as get the full capabilities out of your waypoint management and mapping. Don't expect to just plug it in and everything magically be perfect.
3. The only reason that I bought a humminbird, was that they were the first,,,in my understanding,,,,to come out with the si stuff. Lowrance copied it and has since come out with some really neat stuff.....I wouldn't hesitate to buy either....and I hear that Lowrance may have some small advantages....(use the forum search function,,,as there has been other discussions here on this topic).
Good Luck!
Mark
Here's a few of my OK spots!!!!!!!!!!! ha haha hah aha
3 way split screen with di, sonar, and si
2 wasy split screen with di and si
Just di