I wouldn't do it personally. I do very little highway driving, so my exposure to bugs, pebbles, and the like is minimal. For me, regular washing and waxing are sufficient to keep the car looking good. Obviously wax won't protect against rocks hitting the paint, but I don't have a single paint nick after having my car for 8 months. There are likely clear bra products available I'm unfamiliar with, but the words bring to mind images of dirt lines at the edge between the bra and the paint. These mental pictures are likely of lesser products than you are considering, but I'd still be hesitant to do it. If you're leasing, do you really think that the paint is going to get that messed up in the three year period? If I were leasing, I'd be nearly 1/4 of the way through the lease period, and my bumper looks flawless unless you get really close and start looking for imperfections - and even then those imperfections are rare and nearly invisible.
Another concern about the bras would be scraping the underside of the bumper/nose and the effect this might have on the bra. I'd think this type of trauma would rip the bra and make it more likely to peel and allow dirt to work its way between the bra and the car. Idk, just thinking out loud.
I don't mean to sound too down on these products as I have no personal experience with them. These are just my concerns with this type of protective solution...
650i xDrive Coupe (2012), Carbon Black/Black/Gray Poplar, M Sport, Full LEDs, 20" 373M Wheels, ARS,
HUD, CWP, Premium Sound, Nappa Dash w/ Contrast Stitching, Ceramic Controls, BMW Apps, PCD