I'm not investing in any smart home products unless: * I can fully control them without the cloud on a non-internet connected network * I can either pay for updates, or they have free updates for at least 12 years, ideally 15 If a hurricane or tornado strikes, or some dictator tries to tell me what I can and can't do, my devices need to remain under my command.
I have accumulated so much smart-stuff fatigue, I can't stand anything branded as "smart". This means, as you point out, 1) any outage in the chain between me and the vendor's app shuts everything down for me, 2) stuff behaves inconsistently all the time. (e.g. Bluetooth speakers with a smartphone/tablet player app -- every other time something goes wrong: the app frozen completely because search autocomplete lost pa…
I personally think relays are a much more reliable than solid state switches and are very unlikely to fail in a dangerous way, and fully interupt the circuit, but they do have a 'click' some people dislike, and have a lifetime of 100k-ish switches, so for an application where you keep switching rapidly (e.g. not light switches), this might be a problem.
Ikea used Thread and Zigbee which are not Wifi, they use a mesh network and don't suffer from saturation the way Wifi does, in fact adding more devices tends to make the network more reliable since devices can route around failing or congested nodes.
I've had good experience with them in practice, but do be mindful that they share the 2.4GHz band with Wifi so in an apt building, you might run into radio channel congestion.
Personally I use smart home stuff for controlling heating devices and a few other key items, I don't think it makes sense to make every light switch smart, but technically people have done so and it tends to work all right.