For client your average client? Maybe not so much. Unless of course, your clients are developers.
Well… that’s assuming your target client has no idea that page size has anything to do with speed. That MAY be true… but I doubt it. Everyone has downloaded stuff and everyone knows that.
Now… That in and of itself doesn’t make it useful. You have to clearly explain and tell the story surrounding it in a VERY concise fashion for it to work… which, isn’t a bad thing.
When responsive web design was still new and novel, people had to explain WHY a company would want it. It’s not immediately obvious. I’ve had clients say “Well… my whole page fits inside the iphone… so why change it?”
Just because something is an abstract idea and/or hard to explain, doesn’t mean we shouldn’t mention it.
But… being an early adopter of this sort of feature would definitely be dangerous and I’d get a lot of flack. Still might do it though. I’ve implemented similar things in other sales situations that worked great. Could have backfired… but didn’t.