I'm actually not aware of any plaform that will plain not work for a lefty; in fact there are some upsides for us.
Safety: If your gun has one, it needs to be ambi. The other controls don't.
Slide catch: There are upsides and downsides here. The downside is of course that you can't drop the slide with your thumb, which is the fastest way to do it. The upside is twofold: first, you can't ride the slide catch with your thumb to cause it to lock open or not lock open when you don't want it to. Second, you get to "slingshot" the slide closed, which has the upsides of being more reliable/requiring less fine motor skill, and working exactly the same way on all pistols. I'll admit though as a competetive lefty shooter I was really hoping the Gen4 Glocks would have had ambi slide catch.
Magazine catch: Though it may look awkward to those who have never done it, once you get some practice hitting it with your trigger finger, you will find that this is a pretty good way to do it. Once again, likely at least as consistent as hitting it with your strong side thumb, since for me at least, I think I can get more force on it easier with my trigger finger, and I have pretty big hands. At this point I don't think I'd want it any other way.
So in summary, he shouldn't be afraid and nor should he even confine his search to fully ambi platforms.
If anything I would expect an auto to be more lefty friendly in general than a revolver. With the cylinder swinging to the wrong side, how are you going to reload a revolver quickly? (I'm not a revolver shooter, so there may be an obvious answer to this one)?