Wait, "fall cuts leave wounds open all winter"? That's wild, I always figured the tree was dormant so it wouldn't matter. So the guy was literally fixing damage from the same mistake you were making?

Man, hate to break it to you but that gas cap code and the MAF/O2 stuff are kind of two different things. P0455 is your evap system, so it's usually the cap, a bad purge valve, or a cracked hose, and it wouldn't have thrown a MAF or O2 code at all unless those were bad too. So the guy either read the codes wrong or just saw a chance to sell you parts, which is the part that bugs me... if the only code was P0455 then none of those parts were ever gonna fix it. As for your real question, yes, always ask to see the freeze frame and the live data before you spend a dime, because freeze frame shows what the engine was doing the exact second the light tripped and that tells you way more than a code number alone. For apps, Torque and Car Scanner work fine with a cheap bluetooth adapter, but honestly your $15 reader already did the job Dave needed, so you're not missing much.