My first impression is that doing that to every person he meets is very unprofessional, for one. Especially to every Mr. Johnson. Even if he's doing it entirely in DNI and has no AR visible and doesn't need to move his hands to do anything, he's still noticably distracted, because he is still doing a lot of mental actions. Try holding a conversation or doing much of anything while reciting the table of elements in your head, and you'll see what I mean. There's a reason why they take a Complex Action no matter what.
"Is this even feasible?" There's no C drive in commlinks. Maybe there technically is, but keep in mind this is a sci-fi cyberpunk setting. When they say that a host looks like suburban street and all the files look like newspapers, then each file is seriously a newspaper and you need to go to each one. For a commlink, you can't simply copy the whole thing in one action. Not that it'd be useful, because...
No one of interest keeps everything important on their commlink. Do you think that Mr. Johnson is going to a meet away from the safety of his corp, with a group that he knows includes a hacker, in what's possibly a seedy, dangerous bar, with his every-day commlink broadcasting his real SIN with all the pictures of his family on it? No.
If you're trying to tail someone, sure. Go ahead and waste time downloading his commlink and I dunno, getting some of the songs he downloaded for free. Same with getting tailed and tracing a decker. These people are not morons. A decker should have an Agent running, using Matrix Perception every turn to check for marks and other things-- Think of it like a Host's Patrol IC. And if you're going to waste many turns using Edit File on every image, word document, sound recording, video recording, and whatever else on that decker, he will notice you have a mark on him and erase it. Or worse, start marking you while you're busy faffing about.
As I said earlier, he will almost never find anything of use on someone's commlink. Anyone who has anything to do with the shadows won't be carrying all their important information on a commlink, and it won't be their real SIN either. Anyone who is stupid or ignorant enough to keep all their info on their one commlink with their real SIN is probably just a civilian and won't have anything useful-- Unless looking for a specific thing they have is a key part of the run, or you plan on using a bit of personal information to taunt that one person in particular.
My advice is to make it clear to him that he's wasting his time, and that his employers will think of him as an unprofessional digitial-magpie, too distracted by random contact lists and music libraries to get a job done on time. If he knows he won't find anything of use, and that he is in fact wasting time, he'll realize it's not worth doing unless he's just leisurely hacking some wageslave's commlink...
But remember to let him do it some times. If there's some time between a mission, or he wants to, say... Snoop through a corpsec's commlink for shits and giggles while an extraction is being set up, go ahead and let him. Add some humor-- Maybe that guard has the entire musical history of Oingo Boingo on his commlink. Maybe one took terrible selfies of himself holding a gun in the bathroom. Just keep two things in mind, and tell him as well: If he makes a mistake and reveals himself (failing a sleaze or attack action even once) then he could make the whole run harder for himself and everyone else by causing them to be a bit more alert. And that once the run starts, time is of the essence, because he needs to be disabling security and avoiding detection, lest the Host launch IC or a High Threat Response team arrive.
