Whirlpool with sound system or not

@Rick: Thanks! We couldn't resist

Yes, the maintenance costs also put me off. The topic goes about as well with a photovoltaic system as with a heat pump. Let's see, my wife would really like it that way, especially in the colder months she would probably bathe in it every day...

One can do something about insulation, thicker lid, inset into the floor, etc. to reduce the heat demand. Or use less or not use it at all in winter ... hmm.
is there a control system that is KNX-compatible?

Where are the "big" differences in the various models? The device from HilfeHilfe seems rather cheap, is that only due to size, pumps, etc.?
On the manufacturer's website, the price is in the range of 5-6K€. The also mentioned "Treese Zen" costs four times as much ("Design premium" and apparently more elaborate technology) ...

Jacuzzis or more expensive whirlpools (are then rather designed for long-term use) have a sand filter with backwash, chlorine dosing system, and pH-minus. Water values are monitored automatically. Water level regulation is also available then. UV is only used additionally. Ozone is partially used. Just like, for example, bromine. Saltwater has not really established itself for several reasons (unlike pools). Backwash frequency depends on usage. When not in use, water is only circulated sporadically and the massage pumps are started 1-2 times daily to revitalize the filter medium. Controls with KNX (plug) are not known to me. However, all better ones can be connected to the bus (temperature, pump control, etc.). It's an easy exercise. Theoretically, you can also realize the entire control on KNX.

The Whirlpool from HilfeHilfe is consumer class. Filtration via cartridge filter and manual monitoring of water values... Of course, the pumps also play a role in the price.

With Jacuzzi, you also pay for the name.

Outdoors, the heat loss is enormous even if it is covered and well insulated. I know some who gave up on the outdoor whirlpool. Especially when you have to do many things manually and also the heating costs. Indoors, you don’t have such heat loss but you need dehumidification...

It’s simply a hobby that costs money and you have to take care of it regularly. To a certain extent, a higher initial investment pays off by having lower operating costs and less work with it.

and of course all the others:

What is basically to be thought of the whirlpools from Armstark (Sundance)?
Specifically, I find the model Peyton from the "Klassik 680" series quite interesting.

I would especially like to know what to make of the filtration system.

I cannot contribute any personal experience regarding Armstark whirlpools or spas. The manufacturer has been on the market for a long time. Therefore, it can't be too bad...

The filtration system, as with all "cheaper" whirlpools, is an integrated cartridge filter system (lamella filter). The UV disinfection is more of a gimmick. The water simply does not remain in the cell long enough to achieve a significant effect. Additionally, it requires power, and the UV source would need to be replaced every year. To achieve an effect, it would have to be dimensioned completely differently and would no longer fit into the housing.

As with many things, the question is how much effort one wants to invest. For private use, the filtration system is (usually) sufficient. The water values must be checked very precisely and regularly. The filtration system can no longer save the situation in case of water problems. Since there is not much water in a whirlpool, you can then refill it.

An optimal solution would be a separate sand filter system and direct dosing of chlorine, pH, etc. with automatic water value monitoring. But perhaps only 5% of private whirlpools have this. The maintenance effort is reduced to a minimum, and the filtration system is powerful.