People with little or no experience think they can drill a hole in any valve and make their own constant pressure valve. While this may work in theory, it does not work in real life. We discovered nearly 20 years ago that holes drilled through valve bodies clog up quickly. Small debris in the water can clog a hole at any time. Also water spewing through a small hole at 200 feet per second causes minerals to precipitate out of solution, and forms scale build up. This will clog a hole the same way holes in your showerhead clog up. Also some bacteria love areas of high velocity and will also clog small holes. Either way, what looks like barnacles on a boat hull, quickly build up and clog the small hole. This small hole is responsible for the flow needed to cool the pump and motor. When this hole clogs up, the pump is destroyed in only a few minutes.
To try and prevent the hole from clogging, a much larger hole is drilled, usually about 3 GPM. The size of this hole is also very important. It needs to be large enough to properly cool the pump and motor but, too large and the pump will still cycle at low flow. This means the pump can still be cycled to death and the pressure is not constant. Even a larger hole will clog, it just takes it a little longer.
The Cycle Stop Valve does not have a hole to clog. It has a non-closing seat, with two half moon notches, that come together to create a hole when the valve closes. This allows us to use a very small 1 GPM bypass. When the valve opens, the two half moon notches split, and any debris, scale, or buildup breaks loose and flushes away. This prevents the valve from ever clogging, while maintaining 1 GPM minimum. Now the pump cannot cycle, even when flow as low as 1 GPM is being used. The pump also has the required 1 GPM minimum to remain cool, without fear of clogging the small bypass.
With a genuine Cycle Stop Valve the minimum flow is 1 GPM, so the pump would never cycle while running a 2.5 GPM shower. The non-closing or notched seat of the CSV can never clog with debris, minerals, or bacteria, so the pump would never be destroyed by lack of cooling.
It may look like a Cycle Stop Valve, and be cheaper than a Cycle Stop Valve, but it doesn't work like a Cycle Stop Valve.