You might find a local supplier more competitive on price than Calor. I use Cheshire Gas around here, the bottles are a little smaller than Calor, but the price £ per kg is competitive. The clincher is free delivery, often same day if you call them in the morning,
I have both butane and propane for my heater, I use the propane when it’s really cold as the butane won’t work in very low temperatures.
There are quick release fittings that you can get that fit in the gas hose that make switching the regulators quick and easy. Look similar to those used on compressed air hoses, but are brass and specifically for gas.
I have them fitted to my heater, bbq grill and camping cooker. Makes it easy to use either cylinder on any bit of kit.
If using propane with your heater, it does give off more moisture than butane, which causes me a condensation problem in my concrete prefab garage workshop. Good ventilation essential, for condensation and safe combustion.
I tend to use a cheap Chinese diesel heater for most of my workshop heating needs, which is cheaper to run. But the instant heat of the gas heater is very convenient.