Considering picking up a used 998 si. Does anybody have a pro's or con's ? It does come with all mounting equipment and , transducer.

Good unit. I have ran them since 2010 and I have some great pictures. The 2 D is just ok IMO does not show great arches but the DI/SI are excellent IMO. Easy to use.

I have a 597 ci hd di already , and I love it. I'm assuming it would be the same operating features.

It does, just has Side Imaging too= more views in the menu.

Both versions of the 998 will have an external GPS antenna.
998c SI Combo
998c HD SI Combo

+1 2d isn't worth much but the DI and SI get the job done.

Have 1 at the console and 1 on the bow networked. IMO, the 2d has gotten better with the software updates, I can now "video game" fish and can see my jig/spoon as I'm working a spot. And of course, the SI/DI are awesome to have!

I've had a HB 998 for several years. It is a good unit. My biggest gripe is the screen is hard to see in bright sunlight. Getting a visor type shield helps some. I also like the Lakemaster map chip for the GPS.

I was going to do the same exact thing you are planning on doing a month ago and buying a used 998 si. If you are going to use the unit for a long time and give it good use, don't buy a used one. Get one that you'll own and only own. I opted out of the 998 and older models and got the new line Humminbird recently released, I got the HELIX 7 si. It has si, di, and regular sonar. Just need a micro SD lakemaster card for it and it's ready to go!! The screen is HD and is 7 inches, hence the HELIX 7. there's also a HELIX 5 too. it was too small in my opinion. I'd check out the HELIX series!! I love mine.