The Rebound Air leg hooked up to their plastic frame. Plastic and metal make it a little shaky and wobbly, notthe wobble that adjust the the floor but an unstable wobble that does not feel rooted to the ground.
The Cellerciser has a piano wired spring loaded leg. Most legs that don't screw in are so tight that don't allow for any movement and are very rigid. Notice the difference in the gauge of the springs between the Urban and Cellerciser.
If you are choosing a rebounder with screw in legs, make sure its stainless steel like a Bellicon or a Lymphaciser.
Legs can get stuck and strip it out and once this happens the leg is ruined.

It is best to avoid screw in legs unless they are stainless steel. This is the old version of the Lymphaciser with the stainless steel screw in legs.
Many rebounders have legs that wobble which cause the rebounder to feel unstable while bouncing. Many times this happens over time when inferior steel or plastic structures lose their form through friction from bouncing. The Cellerciser has a leg wobble that does not wobble due to structure loss over time.

1. Screw in type legs are the most stable at first but they can strip out within a few years
2. I avoid folding legs on plastic frames. This has the wobble that I do not like
3. Pop in legs are the 3rd type.  This is the best type and gives the best wobble that adjusts to your side to side bounce.
I strongly recommend getting the legs that use piano wire to hold the legs in.

Leg Testing
Also the feet if they wear out, this can cause one leg to be shorter and the rebounder will wobble and feer super unstable. Polymer that Cellerciser uses on their feet rub away the least unlike rubber that rubs off the quickest of all. If you are concerned about wobble and you have an older rebounder, the Cellerciser Polymer feet also fit on most rebounder legs. 

The longer the legs are the more unstable the rebounder will feel. The bungee rebounders have the longest legs. I strongly recommend the screw in type so there is no wiggle room for unstable wobble. The Premium Bellicon feels the most stable. I recommend the folding leg models if not getting the stainless steel screw in legs. But the most inferior wobble is the plastic rebounder frame. Over time, if the screw in type are not made of stainless steel, they can lose structure over time from the friction of bouncing.

Remember, a little give in the legs (wobble) is necessary if you want to help preserve your rebounder. Most of the problems I hear about are from rebounders that have screw in legs.

The only rebounders I have never had any complaints with the legs getting jammed and can't twist off are the New Zealand Lymphaciser, the Bellicon Premium, and the Cellerciser.

If you need help picking out a rebounder that and have concerns with the type of bounce or a rebounder that will adjust its wobble to your bounce, I will help you choose. Take my rebounder quiz here.
A final note on wobble
Rebounder Wobble is not necessary a bad thing although its a bad thing when its not intended to wobble. When the right wobble is under a rebounder, you should NEVER notice its wobble. 

A proper wobble is mostly to compensate for floors that are not balanced and also to absorb the shock from the frame. If you notice that your rebounder wobbles then its not done on purpose. Chances are that it is poorly constructed.
​Only the Bellicon Premium has the stainless steel screw in legs. I do not recommend any other type of screw in unless its stainless steel. Too many people call in saying one of their legs won't screw back in or won't come off.
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