I fully accept what you say, but dont come on looking for our thoughts then take offence at them when we give you them.
Instead of ‘assistance’ maybe I should have said ‘adaptive’ or soemhting similar. Yes the effect is changed but a variation by changing the exercise might be just as or more beneficial. Highbar/low bar etc for back squats, then you look at depths, foot widths etc as changes.
I just see people in gyms relying on these things rather than learning the proper base techniques.
the Manta probably makes the squats more difficult by having a smaller support area in contact with the bar, the bar being slightly raised up and out. This would create a longer hip to bar lever length thus increasing the work on the back…maybe thats why you feel the upper back work out so much.