Do you realize how big of a HP shot of spray it would be to expend 5lbs of N2O in 3 seconds??!!!
To give you an idea, I run in the lower 11's, and spray out of the hole. 150 wet shot. I use about 2.5lbs of nitrous per pass (I've never accurately measured, but it's a good guestimate).
So to uses some generalizations and simple math, I'd use 5lbs of nitrous in 22 seconds. To use that in 3 seconds, well that's nearly 7 times as much. 150 x 7 = 1050HP shot of nitrous. Ummm, no. Sure, an 8-9 second car might use 5lbs per run, but they are spraying longer than 3 seconds. Also forgot to mention is you can't use a bottle up until it is empty, as you just can't keep the pressure up in the bottle w/ that little in there.
That said, this e-bay gimmick won't work, at all.