This is the important bit, just to amplify the point. If the spring is always in tension, there is always an opposing force on the governor and it will be following a linear change
If the spring lets go, you get step changes from something to zero, then back to something again. Not helpful. You can get this with the internal spring on the more modern Listers
The extra spring in the mechanism is even more likely to give weird results. Putting one spring opposing the other adds the rates together, increasing the force on the governor - not what you'd expect. And if either of those ever goes loose, things will be all over the shop.
Thanks for this stuff, Geoff