I get good images when traveling at 2-3 mph with a matching chart speed of 2-3, if I slow down the images start to blur. I will also say the transducer mount need to be very rigid and lined up well. My 998 HD SI unit was very particular about angle. Also it must be clear of any objects(hull) for the side beams. I tried using the standard RAM mount flex arm thing and it was not solid enough to hold my ducer. Water, debris and such would make it move slightly. I have an older PA - so no Lowrance ready system for me to even attempt. My opinion here - Lowrance and HB side imaging is slightly different. For shallow water( 1-10ft) HB seems to be a little better, beyond that they are both really good. DI on the HB SI units are not as good as Lowrance SS units. HB does not have a dedicated DI crystal and uses the SI data to interpolate the DI image. Unless you plan to spend a good amount of time learning to understand and interpret the SI images and are okay with spending that much $$ on tech you really can't use without constant movement, I would skip it. Screen size is critical as well. My 998 is huge on the yak but I still have to lean toward it to really pick out the details in the SI images. I could not imagine SI on a 5 or 7 series screen. I think it is a neat tool in the arsenal but it takes time to get right and time to understand. Again - my opinion.
I posted my make-shift RAM solution for mounting at the end of this thread: viewtopic.php?f=78&t=46839