Like Dolphyngyrl I've had precuts, even from supposedly high-quality manufacturers, that were amazingly inconsistent even within the same package. I've just finished piecing the blocks for a Sugar and Spice quilt using a combination of my own Precuts (made from my scraps) and commercial charm square Precuts from Moda, Tonga Treats and Riley Blake-- I had to spend a lot of time trimming the commercial precuts because they varied as much as 1/4" in size in some cases within the same package. I had to unpick a number of elements before I realized that the reason I was having a hard time getting corners to match up was that not all of the commercial 5" squares were actually 5" square.
I make my own precuts out of scraps using accuquilt dies for 2" and 3.5" squares, and a rotary cutter for anything larger. I started quilting before rotary cutters were invented and only made a couple of quilts because I got so frustrated with using scissors and templates partly because it is slow, but also because I've never mastered scissor cutting LOL. When I discovered Rotary cutting I got back into quilt making.
Rob