I’ve had the opposite experience with their cloud services in a professional context. My biggest gripe is with United Internet, the monopolistic company that owns IONOS, 1&1 (an ISP) as well as the ad-ridden, flaming pile of garbage that are GMX and WEB.DE, two of the most popular email service providers in Germany as well as a constant source of pain for anyone operating an Email server. They will ignore common industry standards and best-practices, silently block your mailserver for absolutely no reason, not respond to inquiries and just generally make the internet a slightly worse place for small to medium sized businesses and selfhosters.