We borrowed one of these for our first child and decided to buy one for number two. Our first, a girl, loved it and it really helped her legs develop. The second, a boy, has been using it a week for about 15 minutes a day so far and really enjoys the new perspective and movement.
The product arrived quickly in a lot of packaging and is very easy to use and set up. You do need a door with an extruding door frame and ideally plenty of space either side. A double internal door would be perfect. It is very easy to put the child in with two adults and manageable with one. I find this way easiest for a one-person baby-dangle:
1. Set up the frame grips and elastic on your door. Clear the space around.
2. Lying down, put baby in the harness and get him lined up in the middle. Secure the belt buckle.
3. Put the shoulder straps into the plastic spreader-bar.
4. Supporting baby's head with one hand, lift the bar so that the baby is upright, then clip it onto the dangloid.
If the baby is lop-sided, check his bum is in the middle of the harness and that the chest-strap is secure. The package recommends no more than 20 minutes at a time, which seems about right - it is exhausting for the child at first. Don't leave him unattended or let him fall asleep in there.
At first you will need to use the straps to set up the baby so he's just about touching his toes to the floor. Key to the child being able to use it well is when he is able to hold his head pretty straight for a decent amount of time. If baby still has a floppy neck, hold off for a while.
I wouldn't recommend it for any baby which is already a strong or near-walker. With some strength he could slam himself into the door frame. This product can be used as a walking trainer too, as you can see in some of the product pictures.
Overall a good-value, well-built developmental tool for a baby who can hold his head steady.