That honestly seems like a propaganda add. "scare sales" tactic. I buy the orifice part if theres debris to mix with, but an evaporator replacement? Its aluminum and you can flush it out. If you notice part of the story mentions the copper line the one gentleman ran right next to the picture of the green sludge (copper oxide). You should never introduce any dissimilar metals to a system, especially copper to aluminum. All lines, condenser, evaportator, everything is aluminum on my truck as a 93. If you introduce any dissimilar metal parts that will happen too. Everything in there seems to have come from a system containing copper, aluminum is designed for acidic environments as they mention neutralizing the acids that moisture can form. Aluminum is fine down to a pH of around 3.5.
I've never personally had any problems with AC stop leak, on dozens of my own vehicles. The correct way is to replace all orings and possible leaking components, and he did that, so now what? He still has no AC. So if it's already not working, and wont stay filled whats it really going to hurt? Maybe it's leaking as his compressor but then he already needs to replace the compressor... so maybe the sealant will seal it and prevent him from having to buy a compressor. What is the next step you would suggest to him if not using stop leak?