Will RemoteTx software work on a MFJ 1234 RigPi?

Yes, but install it on a separate sd card. Since the MFJ 1234 uses a Raspberry Pi 3b+ internally, the internal sd card can be replaced with a different one that has a RemoteTx image and license key on it. The full featured RigPi has an additional audio card/hat and CW keyer card. RemoteTx can use the RigPi audio card if needed. Many modern radios like the Icom 7300 have audio built in to the USB port which can be used instead of the RigPi audio card. Currently RemoteTx does not utilize the RigPi CW keyer card.

Can I switch back to the RigPi software if I try out RemoteTx software?

Yes, but do not install the RemoteTx software image on the original sd card that is removed from the RigPi.  Use a separate sd card to install the RemoteTx software so that the original RigPi functionality can be restored simply by putting the original sd card back in the MFJ 1234.

Do I have to configure a Mumble client to use RemoteTx?

No. All RemoteTx control and audio features are accessible using a web browser only. Devices that have a compatible web browser do not need to have any additional software installed or configured.

Do I have to modify or configure port forwarding on my home router / firewall?

No. The RemoteTx cloud service makes it unnecessary to expose firewall ports to the public internet. All network traffic is encrypted using industry standards.

Do I need to know the public IP address of my internet connection and if it changes?

No. The RemoteTx cloud service automatically adjusts and re-connects if your IP address changes.

Why does RemoteTx only support several radios?

Each RemoteTx radio interface is custom designed for particular features of that radio allowing a rich control set. The RigPi uses the open source hamlib library that supports many more radios. The control features that the hamlib library makes available varies widely by radio. In the future, RemoteTx may support a reduced feature set using the hamlib library for a wider range of radios. Development of full featured custom radio interfaces will continue as well.