I am currently a Plat 4 Yi main with a 71% winrate using him. Yi can solo carry games if you can play him correctly and don't get to far behind.

During your first clear it doesn't really matter weather you start krugs or gromp. I prefer krugs since in my clear I like to take scuttle after my red and raps. The stun lets you deal more damage to scuttle and stay on high hp as well as get more gold. It also helps since when I back I will have blue buff and will be able to buy recurve bow for more damage and not have to worry about going oom.

Yi's ganks are pretty bad honestly. You should only gank if you have ult, ghost, red, they are pushed, or your laner has good cc. Sometimes after scuttle when you have red you can cheese a kill by going to there buff. Don't be afraid to use ghost it has a short cd.

Yi is a great diver due to him being able to dodge turret shots and able to reduce damage with meditate. During dives you will generally want to be the first to go in with your laner(s) following. You will generally no want to alpha right away unless you are sure you can get a reset. This is important because if there are no minions under tower and you have an ally you can tank lots of the damage but once you alpha the turret will instantly transfer aggro to your ally. When you do this you will want to wait out a turret shot so it wastes one.

Why Rageblade?
Devourer was removed and also well the phantom hit which was moved to Rageblade. Rageblade can be a very good item since it offers AD, AS, and AP. AD will make your E do more AS will let you get more autos which helps your E and AP can let you tank more with your w. The phantom hit will also STACK your double hit letting you get it up more often as well as the phantom hit. Thats a lot of onhit damage. Rageblade can work well with Gunblade since you will be doing onhit magic damage and dealing more true damage which with omnivore (Gunblade Unique passive) will heal you.

Pros
-Good Clear
-A lot of DPS
-Resets
-Can dodge lots of damage
-Mobile
-Fun
Cons
-Squishy (somewhat)
-CC can destroy him
-No CC in his kit
-No built in escapes

Why all attackspeed reds and quints?
Its pretty obvious with my build you will be going more on-hit like and attack speed lets you get more autos off as well as well as your double hit.
Why scaling MR and not flat?
Yi is a farming jgler and less of a ganking. He is more late game and by level 8 you will have as much MR as starting flat.