I'm no help with this conversation. I use side imaging (SideVu) every fishing trip, but I'm not not the fan of it that so many others are. I had a Hbird 998 initially, Lowrance LSS1 later, and now Garmin. I read the Lowrance board quite often and I see no concession there that Hbirds side imaging is better than Lowrance. It may be. I don't know and don't care. I also have a UHD system but I don't use it now as I am focused on water 100-150 ft deep. The first Garmin transducer I bought was a GT51. For people who fish around 30 ft or less of water they would consider this the worst side imaging transducer ever. The front to back cone on 260 kHz is 2.0 degrees. The 455 kHz is 1.4 that I would say is pretty good but other might disagree. But it was exactly what I was looking for and I've not been disappointed. The whole concept of finding fish by first finding structure is something I have abandoned. After reading Buck Perry's book and subscribing to Fishing Facts magazine, I was a fan of structure fishing for many, many years. Now I just skip that step and look for the fish and I find them in all sorts of places, and very often in open water. In my parts, spring crappie fishing for 99% of the fisherman will mean following a bank and casting to shore. I'll be in the open water, out from those same fishermen fishing like I did for umpteen years. My crappie catch is probably somewhere between 5 to 1 and better compared to those fishing the banks and the structure they have found there. My walleye fishing is similar but much much deeper. My tuning of SI is to turn the brightness and contrast up so much that that structure is bleached out so that the fish will show up very bright. My #1 search tool is the Panoptix PS30. My targetting tools for catching are PS22, LiveScope and 2d. If Garmin updated the PS30 to LiveScope level performance, I would pull side imaging off the boat completely. Right now I still need it to get a more detailed look than the PS30 provides.
Don't get me wrong. If you like side imaging and it is that important to you, good for you. I hope you find and get the very best on the market. be it Lowrance or Humminbird and that you are able to find and interpret the structure that is represented perfectly. i'll just keep looking for the fish.