I suppose a lot depends on what utility services you have. A dual minisplit is going to use electricity for both cooling and heating. Electricity is a pretty damn expensive utility (in these parts). You're pretty much stuck with that for cooling but when it comes to heating you have options - natural gas, propane or oil with natural gas being the least expensive. I put my furnace in years ago and only installed the minisplit ac in 2020 but I wouldn't have done it any other way. The Hot Dawg" overhead furnace heats the shop in the coldest weather with no problems regardless of how cold it is outside. But as others have said, the minisplit has its limits both heating and cooling. There is also the issue of failure - if either the heat or ac breaks, is it economical to repair or does it dictate a replacement unit. It would be worthwhile to compare the cost of a single ac/heat minisplit versus an ac minisplit and a separate furnace as well as a comparison of operating costs. The furnace install is obviously a little more involved but much of the work can be done yourself with the exception of the gas line (assuming you were to go with gas). One thing to note with any furnace, it needs an air source or the exhaust will back up into the shop. In my case I just vented fresh air from the attic down through a pair of wall studs.