I feel that the powertwister and other spring devices are very underrated for core strength development and especially wrist and lower arm strength. The chest is not not really challenged that much IMO, if you bench heavy. Arm wrestlers love them .
They require valsalva maneouvre style breathing at an intermediate to advanced level.
This is what a spring looks like with a 10 rep max.
Like everything they are not without their risks . I sprained my wrist trying to get to the next level.
Try these devices at home and travelling. Not marketing or recommending any particular brand.