Weights, weights; I really dislike fluid filled tires. When I was young we had mainly fluid filled tires. Back then there were several people that did tire servicing that would come out and pump out a tire install a boot in the tire patch the tube and refill the tire and you only lost a day or day and halfs work from that tractor but the cost was moderate. Today what is the initial cost of fluid filling a tire? several hundred dollars, calcium is still the least expensive and its quite high, when you get a flat how long and how much to get a service truck out to the tractor ($300+) then add in the cost of more liquid ballast and if you are lucky it will only take 2 or 3 days and several hundreds of dollars to get it repaired and back in service. In contrast if you are using bolt on weights, a slow leak you can get by airing up a tire and continuing to work, or air it up and drive it to a location that is easy to work on it, if tubeless a chance that a simple plug can do the repair and back to work in an hour or so, if it has to be broken down the cost is minimal compared to a liquid filled tire. Add on the poorer ride quality of liquid filled, the horsepower lost to liquid filled, especially if road hauling, the increased braking required with liquid. Bolt on iron can seem expensive at about a dollar a pound but it will cost less in the long run unless you are never going to have a flat, good luck with that if you are farming or doing any woods work, if you are just putting around on a lawn or paved driveway you may not ever get a flat.