So it's similar to a seedbox but with even more utilities? I don't really understand the cache part. It's like they "save" the downloaded files for you?

Real-Debrid conceals your traffic from your ISP by using HTTPS, but the service does keep track of your IPs. It’s best to create the account using an email untraceable to you, pay for the service with crypto or paysafecard and always use a VPN when logging in to the site or streaming

In the megathread it says it is a good way of hiding your IP, but you're saying it isn't totally secure. What exactly is the danger of not applying the security methods you've told?

Yes. I understand. I have only one last problem. I hate subscription services. Although real-debrid is really cheap so if I have to pay for something it will definitely be it. But just to know, are there any free alternatives.

What is that? I've never heard of Radarr not Sonarr

Excuse me, w h a t?