Yes, they narrow vertical dispersion. So much so that standing and sitting too near to them can make a big difference in the sound.
The nice thing is this tends to keep the upper frequencies from hitting the ceiling so readily. In a church or a hall or anything like that it can be a real plus for the acoustics, especially on voice. In a large room at home they can be nice too.

In some PA applications it is difficult to get good sound without using line array. Putting regular speakers on top of each other causes a lot of comb filtering.
My long term goal beyond just having fun, is to create many different designs for home and PA for custom building and perhaps even sales of plans over the Internet. A few years away mind you and dependent on many factors.
If you have questions I would be happy to try and answer. There may be others here who are more knowledgeable and could give additional input.
I'm new to this forum.