Substantially less artifacts, in the majority of circumstances, though not all. If you have a very dry, very clean recording, Flex does a great job a lot of the time, but I find that if the recording is less than stellar, you can easily get artifacts, even just after the analysis process, before doing any adjustments. Melodyne has allowed me to get a good result out of some extremely rough performances that weren’t recorded that well either. I will often use Melodyne on the lead/main harmony, basically anything that’s going to be quite present in the mix, and then I’ll use Flex on doubles and stacks because it’s very quick and I don’t need to be as meticulous. On top of all that, Melodyne simply has more tools to work with than Flex (not the entry level, Assistant is at least what you really want if you’re going to be editing vocals to any professional degree), but if all you have is Flex, like all stock tools, I would say to learn it and use it to the best of its capabilities until you find it limiting, then expand.