The one good HomeKit-capable wall switch you should get
tl;dr: The Lutron Claro (or Diva if you want dimming) Smart Switch is the best HomeKit compatible wall switch there is, period
I've been playing with smart home devices since x10 came out in the 1990s. And every house I've had since 2005 has had a few smart switches hard-wired into my walls. I've tried out almost every brand and heard from several friends with more sophisticated systems than my DIY + whatever is on sale at Amazon approach.
For years, all my friends using HomeKit and Apple devices to control their home have had a a lot of good things to say about the Lutron Caseta line. They are not cheap, usually about $50 per wall switch, and require a home hub you connect via ethernet to your main router, then you install switches that talk to each other using their own wireless protocol, which means your light switches work even when your wifi is down.
To date, I've avoided Caseta because I felt the wall switches were ugly, weird, and cumbersome to use. Take a look at one:
Seriously though, what's up with this wall switch? It's got like 12 buttons and guests in your house would probably have to ask you how to operate it. Can you imagine trying to use this at midnight while stumbling around a dark house?
Eventually, I caved and tried out their most basic switch with two flat buttons, but it was still a tad ugly and not as easy to use as a regular switch. You can see what those look like below:
On the upside, the Lutron Caseta switches I tried out were reliable AS HELL, which is unusual for my wifi wall switch experiences, as they tend to not be 100% available day after day, month after month. Eventually, things crop up and your lights are all showing error messages on your phone and you have to stand up and tap the wall to get any light.
The good news is Lutron finally wised up and made a good looking, easy to operate switch that does everything the old ones did but with a traditional rocker design. Here's what the new ones look like:
They're about $60 each, which is quite steep (plus it requires one of their $100 home hubs) and if you want a very slim slider off to one side to control dimming, it's $10 more or $70 each. Also, you can't buy them at Amazon, only from Home Depot for some (probably weird legal contract) reason.
Anyway, I'm several months into replacing all my various smart wall switches with nothing but Lutron Claro smart ones and even though they're pricey (it's gonna cost about $1,000 to replace every switch I'd like to control from my phone in my house), the installations are going smoothly and pairing them to the Lutron Caseta hub is easy and only takes a few minutes.
Once a switch is set up, it appears in your Apple Home immediately, at the room and name you gave them in the Lutron app's setup. I've been using these for several months now, and I haven't had one iota of downtime, or flaky can't connect messages or any other problems.
I'd long heard the Lutron Caseta line with their smart hub and switches were the most reliable nearly bulletproof HomeKit wall switches and I have to say I agree. I've currently got nearly a dozen peppered throughout my house and they work great in automations (when a garage door opens, our porch lights come on, also ditto for when the sun goes down until about 10pm). I've bought a bunch more and over the next month or so I'm going to replace every switch in a public area as well as overhead lights in bedrooms, so people can turn off a light without getting out of bed (a killer feature in the winter).
I've tried wifi-enabled wall switches from six or seven different companies over the last 15 years and though some can be as cheap as $15 per switch, they relied on custom software and unreliable hacks to get them into HomeKit. With the Lutron setup, everything is native and works out of the box. And so far, I haven't had any downtime at all.
They look and act like normal switches, still have the power of remote control and automations via HomeKit and Siri behind them, and will work 24/7 for years to come. It's surprising no one has made a switch to date with all these features that looked and acted like switches commonly found in homes, but we have them now and I would heartily recommend these for anyone that wants to control their home via their iPhone and other Apple devices.