When should I buy Sword of the Occult or Mejai's Soulstealer?

Solution 1:

I personally never buy them in a PvP situation. It's always a risky choice, even if you're fed. The enemy team tends to focus you if you have a lot of stacks to shut you down.

I mean, if you're like 20/0/0, and it looks like you could kill everyone 1v5, then it would be a nice item to get. As for when you should get it, if you ever are going to get it, get it early so you can stack quicker. As you said, it is really risky. That's the risk you have to take when purchasing stackable items.

However, purchasing the item can be viewed as unsportsmanlike.

Solution 2:

I have to say I almost always buy the soulstealer when I'm playing Normal games with friends that have a lower rating than me. It is a really great gameplay experience if you know how to play with such a high risk item.

But for serious competitive play: Don't Buy it!

It's really only good if you are 100% sure that you're gonna snowball this game and it's a huge wast of gold if you die once. For competitive builds replace the item with another Offensive or maybe even defensive one. But if you are platinum or diamond and you're playing normal games with your bronze and silver friends, go ahead and have fun with the item.

An additional thing: The AD Item isn't that useful. Usually you are better off with normal AD items.