Would the measuring be co-located and are there multiple offices? i.e. are the electric boards close to the gas meter so you are suggesting one EmonTX?
I do prefer the Pi, similar price but far more flexible especially if you don’t want to use emoncms in any form.
As Robert says, the EmonTX in it’s simplest form just outputs serial text, so yes it is possible to send that to a database.
One thing to watch, if the power is interrupted to the EmonTX, the counters reset to zero. Emoncms handles that; you would have to do the same.
In broad terms, I would attach an RPi to each EmonTX. Read the data off the serial using the emonhub subsystem and send it on by MQTT as a JSON data frame to another system to process it for the database (Node-RED for instance). If the optical sensor is required some distance away, then you could just attach that to an RPi and use the same mechanism for the data.
Have a read of this thread (slightly misleadingly titled) Avoiding wireless connections - EmonTX serial RPiZero solution and also this for the pulse Emonhub Pulse Interfacer