I use my phone as one. Pixel 5, and before that a Pixel 2XL. Both were adequately bright, and easily readable. used the P2XL in the gulf earlier this summer. Screen was too small for reading it AND dealing with heavy seas. Also, it didn't like being in direct sunlight the whole time, ended up covering it with a micro-fiber when at anchor to keep it from overheating.
Navionics app works really well and is easily worth the $25/yr they charge for it. It's updated 3 times since I downloaded and started using it in June. You'll want a bigger screen though if you can swing it. Smartphone (5.5"-ish) is too small, and wrong orientation.
I only have a few complaints. First is that I don't get realtime depth, only chart depth. So I only "think" I know what's under me, I don't ACTUALLY know, if the boat had a depth finder otherwise, this would be a non-issue. Would love water temp info as well, again your boat might already have that. I also don't like the "mounted" look. It works, and I get a flush mount setup is WAY harder to make happen, but the giant slab on a stick just always looks like an afterthought. I've seen a few installs where people made a new dash layout and it ALWAYS looks way nicer. Going to have a hard time with that if you use a tablet.
Before you spring cash on a new device; check out this device.
https://www.amazon.com/dp/B08P2SG2NL/ It's $600, but it has an absurdly bright screen, is waterproof, and has a large battery. Found this from the guys that use a tablet in direct sun to fly a drone and needed a bright screen. I would consider one of these as a chartplotter before I would spend that kind of money on a more "consumer" grade tablet if the main use is the boat.