I'm an Android user, and I looked at the Film Photography Viewfinder app, and right below it on my search found the Magic Film Viewfinder app -- for free (likely with nags to upgrade to the paid version, or ads, but I can live with those). I've been using Light Meter (Free) for a couple years, and if you have both open it's pretty easy to switch between them. The meter app has a spot option (it's a bit bigger than 1 degree, more like 5, but it's better than averaging). Then you don't have to wonder if that $30 eBay iPhone is unlocked or not, or learn a new interface (I find my partner's iPhone almost unusable because I'm so ingrained from years on Samsung and Google phones).