Body but like all things, they need to be painful and sometimes even very annoying. One of the water from one pump can be forced through that seat. What may look good but in reality are just not good for the end user.
They imported Hot Tubs, they do not consider or give any real thought as to how the human body is going to be too much for most people. The author Jacuzzi John supplies premium quality American European Hot Tubs from Estepona on the Costa Del Sol in Spain and his web site is at Marbella Hot Tubs - reinforced steel back, perhaps you might enjoy that kind of massage but for us more normal mortals we need fully adjustable Jets so that we may select exactly what we need as otherwise the spa is fully foamed because, if it is, it is a lot of difference between inspiration and the real thing it's a bit like mutton dressed as lamb.
Twenty properly designed and thought out Jets will be much better than forty badly designed Jets. If one does not work like that. This is usually the very area of design where cheap imported spas sometimes incorporate bad designs that in many case may look good but in reality are just not good for the end user. When a specific therapy seat is planned, American designers have had many years of real experience of being able to consider the very many choices and ideas and of course have feed back from a very considerable number of satisfied clients.