The Gel that Danny is referring to may be able to penetrate paper-based wallpaper; not the vinyl or aluminum-type that I refered to. With that, use of a Tiger will most likely only speed up the Gel process. With a Tiger and the liquid-based DIF, you need to do 2 applications and wait 15 minutes between both. The Gel may be 1 application (since it doesn't dry up like the liquid-based DIFF), but you may have to still wait 30 minutes or something. This is another reason I 'question' the Gel, and whatever benefit it presents.
As far as using a Tiger and 'nicking' the drywall, yes, Danny is right. W/O using one, nicking isn't an issue (but we're back to vinyl and aluminum-based paper. With liquid DIF, you need a Tiger.) The paperwork that comes w/the Tiger, I belive, says not to press too hard when you're using it or you'll nick the drywall. One only needs to press hard enough to 'break the surface' of the paper (or vinyl or aluminum.) That's all. And whatever damage one inflicts is quite evident with the naked eye. One either needs to lighten up, or press a little harder. A coat of Primer/Sealer and 2 coats of Topcoat usually 'fill in' any minor nicks. That's one reason I preach the use of high-quality paints from the PAINT RETAILERS; NOT Home Depot. (They're creamier, thus, fill in minor cracks and depressions very nicely.) And if a friend has their eye 2" away from the wall and seeing 'nicks', then they have too much free time!