"I recommend overlapping your batting pieces 6" or so and cutting an "S" shape through the overlap (or several "S" shapes) if your pieces are long. Remove the excess and butt the curves together, hand stitching with a herringbone stitch. Your splice should be invisible in the finished quilt." as stated by Terri D.
I do a modified version of this, maybe not big "S" Shapes, but, kind of big wiggles, and then butt up together and use a zig zag. so far I have had good success with this. I have a roll of the tape and have used it once or twice, but, I find it is not that easy for me - and doesn't always stick all that well. At least that is my experience. I don't have a ridge if the edges are butted up and so far nothing has fallen apart. At least that I know of!!