Proprietary parts are used by manufacturers to increase corporate profits at the expense of you, the customer. They adversely affect your right to repair and take away your right to source competitively priced parts. For the manufacturer, they ensure a highly profitable return because they control the parts distribution and artificially inflate the price of these substandard parts. For you, the customer, it means that replacement hot tub parts are harder to find and significantly more expensive.
They will often market the use of these proprietary parts as a benefit for you claiming superior technology and better quality, but the reality is these parts are lower quality and often are designed with planned failure points to ensure that the parts fail at a regular interval. Even setting aside planned failures and obsolescence, hot tub parts do fail and wear out and you are going to be spending far more money than you should for replacement parts.
This leaves you the customer at the mercy of the hot tub manufacturer who will oftentimes discontinue the parts making small, often meaningless changes so that the part is no longer compatible with the existing hot tub parts forcing you to replace more than just the failed part!
Another popular ploy is to make a hot tub part with other parts built into it, then offer very long warranties on the main part to make you believe that they are superior, but the warranty often excludes the parts built into the main part, and these parts are low end and have a high failure rate. So now your lifetime guaranteed part fails but it's not the main part that failed, it's one of the built in parts that failed so they can avoid the warranty despite the fact that you have to replace the whole unit!
A prime example of this is Watkins No-fault heater. The heater is guaranteed for a long time but the pressure sensor switch is built in and not removable and has a high failure rate. When the part fails it necessitates replacing the entire assembly but because the actual heater has not failed there is no warranty, despite the fact that you have to buy a new heater!
While in some countries that are more proactive in protecting consumers, this practise of planned obsolescence and right to repair is being legislated to prevent companies from using this nefarious practise, in North America there is little or no protection for the consumer so you, the customer, are stuck with higher repair costs and, often, limited supply.
For just how serious this is for you the consumer, you only have to look at what happened to the Appliance industry! Do you remember as a kid your Mom and Dad ever replacing their washers and dryers? Probably not because appliances used to use standard parts that were interchangeable between brands! If your appliance failed a service person would show up and quickly and easily replace the failed part at a reasonable price. Unfortunately the industry went through a revolution several decades ago, where manufacturers started making parts that would only fit their unit and they priced the parts at 10 to 20 times what they were worth! Now appliances last a few years if you are lucky and when they break the repair costs are so high that in many cases they are not even worth replacing.
So now we have an industry that is destroying the environment to build products that are designed to fail and when they do fail, they make a killing because either you pay a fortune for these proprietary low end parts or just throw them away and buy another appliance!
There is no Hot Tub out there from any manufacturer using proprietary hot tub parts that are better than the good standard parts, and oftentimes these substandard parts are 5-10 times the price of the better quality easily available parts.
Several big corporate brands are doing this, including many brands like Hot Springs, Caldera, Endless pools and Arctic spas, who use proprietary heating and control systems and in some cases jetting systems like on Vector 21 brands.
There is not, to my knowledge, any manufacturer actually using proprietary parts for the consumers benefit. They are universally used to cost you money down the road and lock you into a vicious cycle of wasting resources and your money while damaging the environment, with this cycle of broken parts that end up in landfill and necessitate the use of energy and resources to keep making these parts, all in the name of massive corporate profits.
In my honest opinion, there is never a scenario where you should purchase hot tubs and swim spas made with proprietary hot tub parts.