I use the tape sometimes and sometimes zigzag. The trick is to not overlap, butt the edges together.

I use a sewing foot used for making thread flower petals. It has a tall metal finger sticking up in the center of the foot. Use a long wide zig-zag stitch, it holds well and leaves no scar or bump.

I like to piece batting! Call me weird. But last night I made the mistake of not making sure my pieces were the same length.

Just like any other piecing, if one is much longer , you'll get waves and puckering. Hate when that happens.

Don't worry about them being the same length .... but yes, you need to make sure they are evenly fed together and they do not get waves or pucker.

I often join random lengths, then cut the end off.
Often cutting it on an angle, to get a straight edge and then match it in somewhere else.
Or use it to start another section.