Most "purists" hate this kind of stuff because they don't like anything that gives people access without doing it the hard way like they do. People will make comments like "this makes it where people don't even know how to use a radio anymore." Some really old-school purists even hate the fact that you can program radios through PCs (the really, really old crusty Hams) . As you well know, most old-school Ham guys are all about keeping things nostalgic, so they hate to see complex systems that over-simplify the hobby for newbies. That being said, as you've stated, you (in theory) need a license before you would use something like this, so you (in theory) should already know how to use an actual radio before you start doing it on a phone.
Linking repeaters through the interwebs is a pretty cool piece of technology, and can accomplish a lot with very simple equipment. Many, many repeaters are now linkable through the web, and an app like this just takes it a single step further and allows you to access them through the web instead of using a radio as the first step in the process.