David,
Iâve tried the streaming/casting and even wired HDMI option from smartphones and iPod Touches and itâs typically a letdown. Not necessarily for raw graphics but there are âhiccupsâ that break immersion - lag, disconnects, out-of-sync audio.
I typically use Zwift on an iPad with the Tacx handlebar mount (modified with a phone holder for using the Companion App) and itâs just so compact and convenient.
I also have an AppleTV 4k and can vouch for it - if you have an existing TV, Iâd say go that route.
If you have to buy a TV or monitor, the price might creep past that of an Apple Certified Refurbished iPad. Use a site like RefurbTracker to alert you when a unit you want is in stock: https://refurb-tracker.com/
You donât need a current iPad though Iâll let others weigh in on how far back you can safely go and still get reasonable performance. (certainly two generations, maybe more)
If you donât want the iPad on your handlebars (it does wiggle a bit when sprinting, but itâs still secure), there are floor stand options, and you can still have your phone on the handlebars to run the Companion.
Circling back to the ATV4k though: if youâre thrifty and find a used TV or monitor for next to nothing, itâs a viable alternative to an iPad. Oh, I forgot to mention: you can get refurb ATVs as well, saving a few bucks there.
EDIT - while there may be cheaper ways to build a PC, one of the appealing things about ATV or iPad is âthey just work.â I donât think Iâve seen a crash of any kind in 2 years. Click the app icon, Zwift opens and works. No drivers to update, no faffing about with a mouse. No, you wonât get ultra-level graphics but, IMO, thatâs secondary to âjumping on the bike and riding.â