Yes there is some risk of getting your balls sucked in if your cylinder isn't the right size - you have to get the right fit, just like anything else. But when it is right it's not only a 'process' but quite pleasurable - an extension on a regular jerk session!few years ago i was doing like you without ring (2,4 inches large vs 2,5 inches large tube)
balls were entering it sometimes and even if not... it was painful
i had to stop it
but at a point it was pleasant like feeling something different
i dont have youir length by far so not the problem but sad they dont make different lengths