"Retro transitions" has nothing to do with it. What I like about LumaFusion is that it provides 4k support, decent color correction, color grading and multitrack audio and video editing, as well as the ability to crop and straighten clips.
I wouldn't use it on an iPhone, but it's great on an iPad Pro, which has a processor that's better than a lot of laptops.
I do most of my editing on a desktop PC with Premiere Pro, but when I'm away from home I like the ability to do some respectable editing on an app that's as close as you can get to full PC editing software, all on the same iPad I already carry in my Mavic bag to fly with, without lugging around a separate laptop.
If you have an iPad Pro it's a no-brainer for $20. I've spent a lot more on other Mavic accessories that get far less use.
I used to use iMovie but stopped after Apple dumbed it down so much a few years ago. If you're just wanting basics it's not a bad program to learn on. But if you start improving you'll want to upgrade to something else eventually.