Replacing glass only Galaxy S4

So I've done a slight amount of research into this, and the heat gun appears to be highly recommended if not required?
Well, I have a throwaway S4(thankfully), and the glass came off in under 2 minutes with a razor knife easily. Did not cut the ribbon cables, and am 99% sure that the damage I'm seeing inside, was not due to the razor. The adhesive was strong, but I was incredibly patient. I kept a steady tug on it, and it slowly came up. It would appear that it's not adhered to the LCD at all. Unless you count the border of it, where there's an adhesive strip.

I bought a new S4 the other day, and it just fell out of my upper coat pouch pocket tonight. Crack! The glass has shattered. Thankfully, it's responsive in every way that matters. But the glass is a lost cause. Looks like you can get replacements cheap on ebay. Do I really NEED the heat gun? The broken S4 I have did not put up much of a fight to yield the glass.

Ok never mind. Apparently the LCD is more sensitive than I thought.