On this site of the pond...
My family owns 3 Sicomatics by Silit and all of them are stove top units older than 15 years. They all work great and completly silent (as long as one does not use an induction hoob, which generally cause the valve to open a tiny bit). The mechanism consists of 2 valves, one being the cook valve and one the emergency valve. That emergency valve is generally not blockable and not removable. When ever pressure goes severly out of range, that thing opens, but reseals once pressure is back at normal. That never happend to us.
The cook valve has 2-3 pressure settings, dependent of the model. It is used to control pressure, vent the unit and release the pressure. Its usully a sliding selector or a turning dial.
You can use them as a usual pan, so you can use it as regular pot an of course with pressure.
If you pressurerise it, you put everything in and heat it up. Then, you put the top on. Close it (it twists into position) and leave the valve in position close. Once it boils, you hold the release valve open for about 30 seconds to remove any air. Select the desired cooking level and leave the heat high. There is a indicator on the valve that indicates when your pressure level is reached. Once you see it is within range, turn down the heat to a third or less if cook for more than 10 minutes. If you have times of 10 minutes and less, just turn it off.
You can remove the pressure on three ways: First, just let it cool down. Second, you can pull the valve back slowly and put it in the release position. Thats a bit noisy and produces a lot of steam, but rather fast. Last option to cool it down by runnig water over the top. Nothing special there.
Parts wise you need to exchange the lid seal every 5 years and the valve as needed. Both parts are about 10-40€.
We make mostly meat in it, as well as soup and sauces. Its used every few weaks.