The legs that wobble that have a 360 degree wobble like the Cellerciser is the good type of wobble. The wobble from an unstable leg that is not screwed in by piano wire or is one of those fold in legs, this is when the rebounder feels shaky and unstable. When the wobble is the right type of wobble it is a wobble that people don't even notice. There are 2 rebounders that feel so unstable when you bounce side to side but on really high quality rebounders like the Bellicon and Cellerciser, they are super stable on their folding models. I do not recommend screw in legs unless the floor is perfectly even. Screw in models usually that I see end up with a piece of card board under one of the legs to prevent the rebounder from teeter tottering.
Also a good wobble can help keep the feet in the same position when landing so people don't develop a 2-step to regain balance. The Cellerciser has the most wobble and the legs move with me in any direction I bounce in. I notice with rebounders that don't have a 360 degree wobble and most that are screw in that my feet never land in the same position after I come back down.
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.
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.
The wobble on the Cellerciser is multi directional, unlike the other rebounder that wobbles just back and forth at the hinge.
Note: I avoid plastic frames that have unstable wobbles. This is the type of wobble on most of these that I try to avoid. Screw in types do not wobble at all but if the rebounder doesn't have a good frame it can start teeter tottering. The Lympholine and Lymphaciser have screw in legs.
Warning: the non 360 degree wobble type and screw in legs can sometimes make one leg have more stress when the floor is not perfectly even. Usually one rubber foot on the bottom of one of the rebounder legs will wear through and the rebounder can teeter totter. This makes the rebounder unstable and make a noise every time that foot hits the floor. Kinda like a table at a restaurant that you have to put something under one of the legs to keep it from wobbling.
Note: I recommend if it fits your rebounder leg to switch any rubber feet with Polymer feet. Polymer holds up way longer than rubber feet and also doesn't mark up the floor. The Cellerciser has just the right wobble that I have never had to change out the Polymer feet on my rebounder in 7 years to date.
Also, with screw in legs that don't wobble, if they ever get rusty they can get jammed and not screw in all the way. This is when the entire rebounder gets ruined when the rust is on the screw in part on the rebounder, not the legs.
I have the 49 in inch premium stainless steel Bellicon and so far there has been no jamming. The Lymphaciser is a rebounder I would not bring in the rain or any place it could rust. The rebounders I recommend wobble on purpose, not rebounders that wobble because they are inferior and unstable.
I will find out which rebounders have the good wobble and which have an unstable wobble. I will see which ones let me land in the same position each time in respect to wobble as I jump side to side and in all different directions.
Some rebounders are higher off the ground than others and have a higher center of gravity. The lower the center of gravity and the lower the rebounder the more grounded it feels when I land on the mat. It is kind of like the jump stilts I have. I go to the park as much as I can in my Poweriser and Air Trekkers. The Air Trekker are higher off the ground and the Poweriser is lower. I feel way more stable when speed bocking in my Powerisers but if I am simply running and not trying to maneuver my way around the Air Trekkers are the ones I like better. The wobble on the lower center of gravity Cellerciser feels a lot more stable than the rebounders that are higher off the ground.