I just know the basics of it. Users/accounts send 1 Hive to the steembasicincome account, while also nominating another account. Both the sender and nominated account receive 1 share of HSBI. Over time these shares accumulate vote value. Once it reaches around 0.02 in value, the SBI account will vote on the next post of the account. What I like about it is that it continues to accumulate even if the account is not active. If one went on a vacation, it still continues to accumulate, so that when they post after their return, they can receive a much bigger vote. Here is my current status:
When looking at it from a comment upvoting perspective, I think their method can work well in determining the minimum vote is reached first so it isn't wasted. The accumulating value also doesn't penalize users that are not as active in upvoting comments, compared to the beneficiary option. Buying shares also makes it easier to control the contribution since everyone is getting the same thing. With the beneficiary, some might be hesitant especially if they sometimes get a big vote on their post.
Some of the cons I can think of is that I don't know if it is easy to scale to upvoting comments which is significantly more than just posts. Additionally, whales can take advantage of it if the vote amount accumulation is calculating based on all shareholders.