I've purchased a few bags of loose fill cellulose insulation from the local hardware store (GreenFiber brand). How will the insulation work if I don't put it through the machine to fluff it and force it through a tube? Will the insulation be compressed a bit so that I won't get the coverage that the bag says, but its R value per inch should be about the same? Can I consider its R-value to be something close to the "dense-pack" R-value?
Since cellulose insulation is compressively packaged you cannot install it without using a blowing machine. I do not recommend trying to do this by hand. "A few bags" may not qualify you for loan of a machine, but you can certainly rent one from a big box home center or an equiment rental service.
The R-factor of fiber insulation follows an inverse "U" curve. As density increases, R-factor increases--up to a point. Dense packed cellulose insulation at 3.0 to 3.5 pcf--typical installed density in closed cavities--has an R-factor of 3.9 or 4.0, compared with 3.7 or 3.8 at settled density. Fiber glass at 2.2 to 2.5 pcf may have an R-factor in excess of 4.0, compared with 2.2 to 3.1 at design density. At some point the curves for both materials turn around and R-factor decreases with greater density. For cellulose that seems to be somewhere between 3.5 and 4.0.
That type of insulation comes highly compressed, blowing it in will get separated and back to its original size. Without decompressing it the insulation won't have any air space, so less insulation value. You will end up using more insulation material and spending more money for less insulation capability.
Additionally without a blower you'll have trouble getting it actually dispersed into your wall in the first place. Blowing it in will get it spread out evenly, simply pouring it in will likely leave large gaps, meaning less actual insulating.
Next you have the time factor. blowing it in is quick, but if you do it manually it's going to take much longer. First you'll have to find a way to decompress it fully, then lift it up to the hole, then push it in the hole, then manually disperse it somehow.
So can you do it without blowing it in? Yes, but it will take much longer to do, cost more in insulation, and not be as effective in insulating your home, meaning more money lost over time.