(1)I run a mini split HVAC in my shop and I live in Kentucky. Works wonderfully in keeping my shop warm in the winter and cool in the summer.
edit: (2) I am not sure how it does that being that it is a heat pump, but for some reason these mini splits can produce heat without resistive backup heat strips down to(3) ver very cold unlike traditional HVAC heat pumps like I have at my house. Very nice, constant heat and the beauty of these things is that they are inverters and it can put out 1/2 ton up to 1/5 ton based upon what the demands are....(4)unlike a traditional single stage HVAC that blasts you with basically full on or full off.
(1) while I agree a minisplit is a good solution for heating AND cooling, there are a couple of drawbacks in installing a minisplit to heat a garage or shop. Namely that the majority of minisplits lack the cfm needed to properly heat a large area and do not create enough airflow. The benefit of a central HVAC is that there is a supply and return which simply is receiving pre-heated air and adds heat as opposed to heating up the air from scratch. This is where their efficiency comes from as opposed to minisplits. In order to make a good and efficient minisplit system where would need to be something else that circulates air better...
(2) they essentially work by being a pump.. for heat... the heat pump is essentially the same as an AC with the flow going the other way. Meaning the outside coil is cooled and the inside one is hot. It not only gets the heat from the surrounding air (despite it being "cold outside, there still is some "heat" yet there is less of it. Essentially there is no such thing as cold. Just a lack of heat). The coil heats up because the fluid loses its compression and due to friction. When compressed the fluid becomes cold, the heat pump just decides where this cold fluid goes. Inside for ac or outside to heat the inside.
(3)most mini splits only work until about -12 or -15 C which is 5f to 10f. There are models that will go down to 0f but most of them lose the majority of their efficiency around the 20f. While they still work, the amount of electricity needed to extract the heat increases and there are chances that the outside coil freezes over, causing the unit to simply shut off.
(4) while most HVACs are single or step stage, there is a point/benefit to it.
That running for half or full blast for x minutes is better than a unit always hunting and sending off 10% then 50% then 20% then 70% then down to 5%, while this promotes constant airflow, it is usually insufficient for the whole house or shop, as it can only measure at the thermostat, meaning one place will be cold and the other hot and where the thermostat is, it will be the set temperature.
The only way to fight this issue is by AIRFLOW which is key in a shop or garage to circulate as much air as possible and slowly heating it up.
Not only is the cost sometimes an issue with the minisplits and installation, it doesn't guarantee frost protection as the unit may freeze over.
A good minisplit will have resistive elements and "auxiliary heat" which are either elements or a function that reverses the unit to thaw the outdoor coil, but that again increases the cost of the unit and complexity.
I think OP is better off with two electric heaters due to their lack of maintenance needed, one to maintain the heat and the other to help with airflow or to help bump the heat up when they are working in the shop. After a year of use, they will be able to judge whether a gas line could be beneficial or not (sometimes it isn't, it depends on the price, consumption, etc).
On a side note, for summer a simple dehumidifier/air exchanger will help keep the shop colder and in the winter easier to heat. If OP or anyone is interested I can explain the design which is pretty much DIY for about 100-200$ depending on the size of the garage. It's pretty much an inline fan with some ducting and a humidistat.
