I own the GOBig Electric - had to go to it because between my hands and back I can't dod much with a rotary cutter. By now I have a bunch of dies - I try to buy them only when they are on sale or on clearance. I have a couple of the Cube (6" and 12") boxed sets, but there are sometimes duplicates if you buy too many boxed sets so I now buy mostly singles. I try to buy the pieces that will work together (3", 6", 9", 12") so I can mix and match pieces to make blocks. If I find a block I like that is 8" or 10", I try to modify it so I can use what I have.
I, too, prefer the dies that cut multiples of the same size piece - that way I can use large pieces of fabric and finess it so I have minimal waste and a limited amount of hand cutting. The BOB (Block on Board) that have all the pieces for a block are a pain since I don't want all the pieces of a block in the same fabric and it is annoying to have to cut the fabric small enough to cut all the pieces in the correct color. For me, minimzing waste is a game I play and with the fabric stiff, even if the grain is a bit off it doesn't affect the finished size since even when sewn there is really no stretch.
There are several tricks to minimizing waste. I starch my fabric so it is very stiff. As soon as I get a die, I use the very fine tip sharpie to mark a 1/4" line around the blades. I have found the combination of stiff fabric and a little extra around the blades keeps most of the fabric from slipping into the space between the blade and the spounge surround.
My biggest complaint is the mats - they are expensive and they wear out. Again, I get creative and I move and rotate the mat so I have slits all over and maybe some holes before I replace it. I have found that as long as the mat covers the blades any direction works. Mats rarely go on sale but when they do I stock up.