there was no well-known German brand for air conditioners called "Felsen." It's possible that the brand may have emerged or gained popularity after that date, or it might be a relatively new or niche brand.
When considering the quality of an air conditioner brand, it's essential to look for factors such as customer reviews, product specifications, energy efficiency, warranty, and after-sales service. Additionally, established and reputable brands tend to have a track record of producing reliable and efficient air conditioning systems.
If "Felsen" is a new or lesser-known brand, I would recommend conducting thorough research, checking customer reviews and ratings, and seeking expert opinions to determine if it's a good option for your needs. Additionally, you may want to compare Felsen's offerings with those of more established German or international air conditioner brands to make an informed decision.