Oh, it's very useful, but it'd corrupt most people - but if I could control when I was invisible and when I was not, I'd spend money, sure.

in a heartbeat, it would be incredibly useful, for legal and immoral reasons

It'd be great for the military. And you better believe people would buy it! for hollywood, for pranks, for whatever, you name it.

It could be very useful ... and dangerous ... and embarrassing.

useless many people spend their lives feeling invisable so who would want to buy it

haha i would use it to get out of that one teachers class who you hate with your guts lol some might also using for stealing purposes

It is not at all useless, but there is a cheaper choice: "The Somebody Else's Problem field (SEP field) is a fictional technology from The Hitchhiker's Guide to the Galaxy "trilogy" by Douglas Adams. It is a cheaper and more practical alternative to an invisibility field." "An SEP field is a generated energy field which affects perception. Entities within the field will be perceived by an outside observer as "Somebody Else's Problem", and will therefore be effectively invisible unless the observer is specifically looking for the entity. This effect is greatly heightened if the entity within the field is already unexpected or out of place. The primary example of this was given in the third book Life, the Universe and Everything, when a spaceship built to look like an upside down bistro utilizes a SEP field to land unobserved in the middle of Lord's Cricket Ground. Another example occurs when the aforementioned ship's field is extended so that the characters fail to notice the fact that they cannot breathe or the fact that the asteroid that they are standing on does not have enough gravitational force to hold them down, and thus are able to breathe and stay grounded. It should be noted that a SEP field won't render an object invisible if it is expected to be there, and an SEP-cloaked object may be noticed out of the corner of the eye. The SEP field requires much less energy than a normal invisibility field (a single torch battery can run it for over a hundred years) due to the natural propensity of people to see things as Somebody Else's Problem." Source: http://en.wikipedia.org/wiki/Somebody_else%27s_problem_field

Well if you could change back and forth.......just consider the possibilities!

If I could activate it and turn it off when I wanted to, then yeah, I'd buy it for sure : P It would be great for all sorts of things...

It's useful but really depends on how it works. If for example it bends light around you...you'd be blind as no light would reach you. Also it would need to be able to be turned on and off. As shown in the film "invisible man", I'd really hate to see my dinner digesting or not be able to sleep because I can see through my eyelids all the time. The other reason it would have to turn on and off is to socialise with people and the such. But more importantly so you can look after yourself. You'd be hard pressed to treat yourself if you got injured and your cleanliness would require extra work as you couldn't tell if you'd washed that part or not.