This would indicate (as with revival) that it constructs the individual via their 'imprints'. Is it not possible Gantz created the 'aliens' and technology to prepare certain individuals for an attack of another faction? Interesting theory, but likely incorrect, yep.
You underestimate their tactical prowess at logically pinpointing the location of an invisible target. :P Additionally, when it becomes evident the assailant is invisible, there will be extensive transportation of valuable people via intricate plans which are difficult to observe simultaneously...
You'd easily be stopped with a missile strike via an unobservable drone, but they might simply neutralize you to preserve the suit for reverse engineering. :p Ideally, a user would become an incredibly proficient contract killer, I think, or intelligence officer.
You have four choices: two fictional Gantz players and two individuals from this board. My choices would be:
Kei Kurono - Highly skilled, concerned with team progression, and fairly reasonable.
Masaru Katou - Kurono's partner- essential to manage him well wwith morality. Combined, I think...