if you have a modern cylinder and a modern boiler, it will heat the cylinder in about 20 minutes. depending on bathroom usage this can mean that by the time the first person has towelled off, cut their toenails, brushed their teeth etc, it is hot again.
a pumped power shower can deliver a great deal of water, so if the first users drain the cylinder, there will obviously not be much left for the next user. If you get a bigger cylinder, there are some people who will just have a longer shower so they will use all the hot water from that, too
I stayed at a place in Australia where each bathroom had its own hot cylinder, thus preventing any one user from hogging all the water.
BTW it will be very useful if you run the power shower into a bucket and calculate how many litres per minute it delivers; then put the bucket in the kitchen sink and see how many litres per minute you get from the cold tap.