Been using the a7S III for a long time now and honestly you have a couple solid paths depending on your workflow. If you want the industry standard, go for the Atomos Ninja V 5.2-inch 4K HDMI Recording Monitor. It handles that 10-bit 4:2:2 signal perfectly and gives you the option for ProRes RAW if you ever need it. The 1000 nits is decent, but can struggle in direct midday sun without a hood. If you dont care about recording and just want the best software tools, check out the SmallHD Indie 7 7-inch Touchscreen Monitor. Their PageOS is miles ahead of Atomos for technical stuff like false color and framing guides. Lastly, for pure daylight visibility, the Portkeys BM5 III 5.5-inch 2200nit High Bright Monitor is a beast. 2200 nits means you wont ever need a sunhood. Just watch out for the fan noise on high brightness settings tho.

Just catching up on this thread. If you want something super bright without the recording price tag of a Ninja, look at the Portkeys BM5WR 5.5 Inch 2200nit HDMI SDI Monitor. It is a daylight beast at 2200 nits. Pro tip: always get a high-quality Zilr 4K HDMI 2.0 Cable because cheap ones will drop that 10-bit signal constantly and drive you crazy.

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Honestly, congrats on the a7S III, that is such a beastly camera. I am still kinda figuring things out myself, but I had the exact same issue with the tiny screen when I first started using it. I think I heard somewhere that you really need something with at least 1000 nits if you are shooting outside, otherwise you are just squinting the whole time and guessing. I am not 100% sure about the technical side of the 10-bit stuff, but a buddy told me that some of the mid-range monitors can actually handle the signal from the Sony just fine without breaking the bank. I personally went with a 5-inch one because it keeps the rig light and easier to carry. It has been a total lifesaver for focusing. IIRC, you might need a really good high-speed cable too because the standard ones flicker sometimes. Just my two cents as someone still learning the ropes tho!

Saving this whole thread. So much good info here you guys are awesome.