If you think a device with storage mechanism that can simply connect to another computer and view all your keys is safe enough for your communication needs, then it is fine, you don't need to use Signal.

People use Signal because they don't want to be compromised when they just leave their phone / laptop unattended for a couple minutes on a bus or a train. They don't want to be in a situation if one day their laptop gets computer virus and they have to assume all these accounts are compromised and have to restart their digital identity all over again.