We had a glider when our children were first brought home. Sometimes you have to sit up / sleep sitting up with them all night or at least every 2-3 hours for feedings. We both thought, "oh, it's like a rocker but better!" because we were young, stupid and believed advertisements.
It's nothing like a true rocker. The motion in my opinion is just...wrong. Instead of nice, gradual acceleration-deceleration, you go through the weirdest double hump of speed. And, it's much harder on the knees. Mechanically, it's far too complex. All around, I would say - again in my opinion based only on my experience - that it's nothing more than a gimmick and doesn't hold a candle to a true rocking chair, which can be very soothing.
We ended up getting rid of it when we realized we hadn't sat in it even once in the five years since the last child first slept through the night.
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“For small creatures such as we the vastness is bearable only through love.”
―Carl Sagan