Right now, it feels like MULEs are only used out of desperation or if the prices of everything else have gotten insanely high. This is true despite a number of players expressing surprise when I mentioned that MULEs required fuel. 

Now, there's nothing wrong with having very niche black market items like the MULE, Network Virus, Core Sample, and Circuit Overload, but it feels like a problem that MULEs are already ignored and are actually worse than most players think. As far as I can tell, MULEs consume a constant 0.2 fuel per second while they're active, regardless of whether they're traveling to a tile, returning from the tile, or extracting resources. I believe they move at a speed of 1.2 tiles/second and assuming they extract resources at the same rate as a mine/quarry/pump otherwise would, a high resources 12 tiles away from your HQ would take 300 seconds (over 2 Sols!) to finish collecting the 200 of the resource it's designed to collect, consuming 60 fuel (20 from extraction, 40 from travel) in the process.

An equivalent mine would consume 0.2 power/second, so the constant cost isn't that crazy an idea, especially given that you don't have to spend a claim. Still, the mine would take 15 seconds to fly out, 20 seconds to construct, 100 seconds to produce the same 200 resources, and 12 seconds for the final shipment to arrive, giving a total of 147 seconds to collect the same amount of resources as the MULE. In the process, the mine will have consumed 24+3 fuel and 20 power (pretending you turned off the mine the instant it finished collecting the 200 of the resource). 

Lower resources would represent a 0.2 fuel for 0.2 power tradeoff while farther resources represent a tradeoff between the MULE extra speed and additional fuel cost for travel in both directions (too lazy to do the algebra). In any case, even though MULEs save you from committing a claim and are resistant to pirates/magnetic storms, I don't feel the cost/benefit is where it needs to be, especially given the upfront costs of the MULE (cash and a black market cooldown). The fuel consumption of MULEs can even be very problematic since they can't be turned off, so a spike in the fuel price could be incredibly painful.