Numitrons are essentially filaments like in lightbulbs versus discharge of a cathode and gas. I personally chose the numitrons because there was a pre-existing open source project for it and that it uses lower voltages.
I personally want a 6-tube design, however the PCB I chose doesn't really support that, and I don't want to learn how to make changes to a pre-existing PCB or have to make a new one. This would also require rama (or someone else, probably myself) to make edits to the case, and finally, I am going to source the tubes from eBay, so it will be quite annoying to have to get more tubes. HOWEVER, if there is enough interest, I will be fine with doing all of the above.