My 2021 SX210 provides depth and temperature on the Connext screen. You don't have that on your boat?
IMO, the depth gauge is not reliable long-term. I have no idea if it's the way they set them up, the equipment they use, or the software. Looking across the forums, it isn't consistently consistent. I have no idea on the temp gauge, but depth...look for yourself, you'll see what I'm talking about. I've got depth and temp, and I don't trust either of them.
I'm good with the depth on the Navionics app for the water I boat on, no experience with strange waters utilizing the app, but there's a comfort level that's acceptable for me. Each person has their reasons for wanting something better, or believing they've already got a solid plan.
I will say that if I believe if you've got a 19', a 10" tablet is going to feel like a 55" flat screen TV in your bathroom. I've got a 21', and tried my old 7" tablet. To me, it was too small. An 8" MAY have worked to my satisfaction, but the 10" Samsung Tablet works fine for me, and it doesn't feel too large to my tired old eyes. The nice thing about a 10" tablet is that you can turn it sideways (landscape mode), and it'll fit nicely above the dash and protected by the windshield. I've got it in a Unicorn Beetle case with a glass screen protector, and it works great. I haven't been caught in a downpour, but I have been rained on pretty well, and the tablet survives to this day, unscathed. As for heat issues, while I'm in motion, it doesn't seem to be an issue, and when we come to a stop, throwing a towel or shirt over the windshield should be enough to stave off heat-related issues. Throwing it in a lighter colored case could help the situation as well.
I just can't stand the fact that the boating-specific solutions like the Garmins are so dang expensive. There's a disconnect in my mind as to why it's somehow worth 3-5X the cost of my redneck solution (which is still spendy enough!). Seems like they could make a fortune selling something similar to the tablet without all the fancy stuff thrown in that the non-fisherman either isn't going to need on the regular, or doesn't want the added options.