When they are practical to use in your environment, ultra short throw projectors offer some great advantages, and a disadvantage or two as well.
First of all, unlike projectors sitting 8 or 12 feet from the screen, a UST projector like this Casio won't blind the presenter if they move in front of the screen (which certainly happens a lot). Being attacked by a very, very bright light is not pleasant, and it can be a major distraction to the teacher or presenter. In addition, the speaker is not casting a shadow, blocking the light from the projector from reaching the screen. Those are big advantages.
If the projector is going to be installed, there's also normally significant savings compared to longer throw projectors. The primary reason is that this Casio will mount to the wall, directly above the screen surface, rather than hang from the ceiling. That means the install work takes place on just one wall, along with the screen. No power and cables to run up to the ceiling. There's an installation cost either way, but it definitely should be a good deal less with an ultra short throw projector.
Another benefit is sound, which normally comes from a rear facing speaker. The entire audience is behind the projector so the sound is going where it needs to.
But, as I said, there are a couple of downsides as well. The first one, is that UST projectors, including this Casio, tend to be significantly more expensive than longer throw projectors.
Another limitation is image size. Because of the unique types of optics used in UST projectors, you normally don't get the ability to project to any size you want. Sorry, no 15 foot image size with this projector. Casio only states up to 110" diagonal. Of course, that's plenty for classrooms, conference rooms, training rooms etc. On the other hand, that won't cut it presenting to 300 people in a Marriott hotel ballroom.
Maintaining very good sharpness across the image, and a reasonably evenly illuminated screen are often challenges for UST projectors, but the Casio is pretty sharp, and the amount of roll-off to the corners is relatively minor compared to some other UST projectors.