I read most of this over the last week and a half and had my mind blown. I've been playing 5e for a few years now, and I've run it a handful of times.
Pro: ICRPG is familiar for anyone who can play 5e and easier to learn for anyone who's never played a TTRPG before. For a one-shot game, I'd recommend this over 5e any day. You can build a character in less than 20 minutes and you don't have to worry about optimizing. The system is (really) setting neutral, and the book includes 5 settings that work with it and are fleshed out enough to run. It also has excellent GM advice and guidelines for building monsters that will open your eyes permanently.
Con: The first is kind of obvious, because it's the converse of the pros. Because it is so stripped down, it will not appeal to min-maxers, and anyone who thinks 5e is already too simple will want to throw this out the window.
The hearts system, which Brandish/Hankerin/Runehammer claims is revolutionary, is dumb. A heart represents 10 HP, but you still have to track HP. You just stack them in bunches of 10 when building NPCs. It's a layer of abstraction that adds nothing.
The last con is more severe. The book is much better organized than ICRPG 2e, but still baffling at times. If your players try to read through setting information, they'll run across things that are intended as story hooks for the GM and are not labeled as such. It's kind of a mess.
All in all, though, a game that lets you get up and running in at least 5 different settings this quickly is worth a recommend. Take what you like, throw away the rest, and have fun. My group sure did.
[4 of 5 Stars!]