I've read into the Saga phone the other post mentioned, and it does seem to service the market of people who want all four of security reliability convenience and mobility when it comes to hotwallets.
It looks like the phone uses Qualcomm's latest technology on a secure chip. If I read it correctly, this won't be an exclusive technology for some manufacturers, so I won't be surprised if there will be more apps that support it in the future. The point is, it is not gonna be hardware or software exclusive, so I'd rather wait and just use any Android phone with open-source apps to manage my crypto right now if necessary.
Most of these hacks are done via phishing or social engineering anyway. A secure device won't help you at all if you just give your password to whoever asks you.
Also, the question "why cram so much into the phone", has been asked so many times for the last 20 years. Humanity doesn't seem to care, and seems to constantly deviate towards innovation when it comes to smartphones.
You can certainly add more features, but it also adds more attack vectors. It might work, but it will always be riskier to use compared to a dedicated device that is designed to cater to specific needs IMO. Don't know how balanced it will be but I personally don't want to risk security for extra mobility. I never bring my HW outside of my house or when I travel anyway. If I lose it that will be a disaster.