Roller Trees

Hi dudes
I got a pair of roller trees and as I was looking at them I
could not figure out why they would be any improvement at all!
The 2 rollers are press mounted on the the same pin.
So if you turn 1 roller, they both turn. They don't spin
seperately..
If you stretch the G string the G roller should turn a little but the
D string is is planted up against the other D roller stopping the G roller from spinning.

The G is more less just "SLIDNG" under the G roller and it's not really turning at all...
Am I right about this
shouldnt the rollers spin independant of each other? or wat is the point of these?

Strats for Life..

I've never used them- I feel like less moving parts is a better approach. I suppose if a roller string tree works at all, it's better than nothing, even if the G and D string move together, at least during vibrato use.

The ones I used were independent of each other.

thanks guys
ill try staggered locking tuners and no trees