If there is nothing wrong with your friends cranks right now, then he should be saving his money. I don't recommend that anyone spend $80.00 on so-so product when for $100 bucks you can get an awesome product via the Internet or on eBay used. I definitely don't recommend replacing perfectly good 1-piece cranks with perfectly good 3-piece cranks that aren't any better at all.
It's like buying a desk from Ikea to replace the desk you got from Target. They both are low end desks that cost 100 bucks and will wear out much quicker than a high quality desk from Ethan Allen that costs 400 bucks. (weird paralel, but I couldn't think of anything)
Anyway, many 1-piece cranks are 4130 chromoly and are of very good quality and perfect for smaller riders. Your friend probably won't break your 3-piece cranks, but he also hasn't broken his 1-piece cranks. As the saying goes: If it ain't broke, don't fix it.
Save your cranks until someone actually needs some cheap cranks, then sell them for 20 bucks to that person.