A pressure balance shower control consists of one handle that controls both volume and the temperature of the water. A two-handled pressure balance shower has one handle for hot and one for cold. The major advantage of a pressure balance over thermostatic is price; pressure balance showers are more cost-efficient. The downside is that you get what you pay for. With pressure balance you have fewer options for your shower. A pressure balance value will not allow you to use more than one function, like an overhead shower head and a handheld shower or body spray, simultaneously. Because it cannot sense temperature, the scald-proof factor is lower than in thermostatic systems.
A thermostatic shower does as it implies: it keeps the temperature stable. Thermostatic valves sense water temperature and will mix the hot and cold to deliver the perfect temperature. Once you find that temperature, you won't have to find it again every time you shower. This is the “set it and forget it" feature of thermostatic. Because you control two shower components, the volume and the temperature, thermostatic values have two handles. One controls and perfect temperature and one turns the water on and off. Thermostatic values have the advantage of being safer for children and the elderly, who are especially at risk of shower scalds. It's also great for the lazy and busy people who don't want to fiddle with the temperature every time they shower.