node-red-contrib-rfxcom developer Max (not Hastings!) here. I can confirm that you can use node-RED to control Somfy 'RFY' or 'RTS' type blind motors with 434 MHz receivers using the RFXCOM RFXtrx433E or RFXtrx433XL transceiver modules. They have a USB 2 interface, which uses an FTDI chip to implement a 'virtual' serial port. Windows, Linux, and macOS/OS X all have drivers built in, nothing extra to download. You can run Node-RED on any of these operating systems, and the
node-red-contrib-rfxcom will find the transceiver and connect to it, so long as you tell it the correct com port or /dev file. There is a script provided to search all serial ports for transceivers, but it is generally easier to look through the operating system's list of serial ports to find the one that appears when you plug the transceiver in.
I don't have Somfy blinds myself, but I know there are
node-red-contrib-rfxcom users who do, and with success. As far as I know, you can use the conventional remote in parallel with the transceiver - it's just another remote control as far as the blinds motors are aware. It is paired with the motors in a similar way to a normal remote, as described here. (you can transmit the program command by sending a message to the
rfx-blinds-out node with payload of 'program')
You can send stop command from node-RED, but as far as I know you don't have to, the blinds will stop in the fully up or down position automatically.
You don't need an Internet connection - it's all local to the machine that is connected to the transceiver.
node-red-contrib-rfxcom is actually a wrapper round
node-rfxcom: a general-purpose node.js package of which I am also maintainer and main developer