is it worth it?

OK so lookin to upgrade to a GPS ff and and wanting to stay with hummingbird but a lot of their GPS ff have the di or si system and the thru hull transducer isn't compatible with those so is it a waste of money to buy one or not?  Have a 343 which is GPS ready just doesn't have the internal antenna on the combo units.  I realize the easy thing would be to install a GPS antenna on the yak yet don't know how durable they are.

This might help

http://www.kayakfishingmagazine.net/articles/139-kayak-fishing-how-to-articles/1822-down-scan-imaging-down-imaging-shoot-through-demystified.html

I find down imagining a really useful tool for identifying structure when vertical jigging. Otherwise I run 2D. My recommendation is to make sure your not limited to DI and can switch between the two. If it's one or the other stick with 2D

IMO an integrated GPS and/or antenna is the way to go. We already have so many little things to rig and manage most of the time. An external antenna just adds to the mix.

I run a Humminbird SI unit and it amazes me what I can see on the bottom sometimes.  I use an over-the-side transducer mount so as to avoid any attenuation that is caused by shooting the signal through the hull of a kayak.  The over-the-side transducer mount is a pain to deal with.  It's noisy, slows me down a little, it catches weeds, and I have to have one more cumbersome thing mounted on the deck that could get tangled up in something.  But I put up with all of that because having that crisp side imaging signal is awesome!  It also does down imaging, regular sonar, and has a built in GPS that doesn't need an antenna.  So to answer your question, yes, in my opinion, it's worth it.

The GPS feature is totally worth it in my opinion, especially for salmon trolling.  I used to use a handheld gps with my old FF, but again, it is one more piece of gear to lose/have to remember.