I'm now using a metal mount for my $140 Moto X4 - search on 'universal bike phone mount metal' (no quotes); I'm pretty confident my phone won't be lost.
Meanwhile, the X4 has a bigger screen than any dedicated computer I've seen, and it's readable in sunlight and under clouds. Lots of apps provide metrics; and because I don't turn on data or spend hours on the phone, I get great battery life. I tried using my retired Galaxy S4, but I can't read the screen when it's sunny.
Would I like a Garmin 520 or Wahoo Element or even something like a Lezyne Macro? Sure - but I can't justify the expense. If only the bike mount looked unreliable! If only the X4's screen were unreadable....