Coconut oil when I have it - a bit of canola oil when I don't. Those plus olive oil are the only fats I ever use to cook with. Air popping of course would be the best way to go but I just can't enjoy air popped corn like I do my old fashioned popped on the stove corn method.
We use something similar to this :
Have to add butter to the popcorn after, even if it's just butter flavored spray, so the salt will stick.
I would probably prefer just the bagged microwave popcorn, it's easier and less cleaning, but my employer has the popper, so that's what we use.
Read my post #31588 - that microwave stuff is not at all healthy.
I add the salt immediately after the corn is popped. There is just enough hot oil and steam on the corn so the salt sufficiently sticks.
I do like the looks of your popper but how do you stir it and how does the steam get out? Mine is like this one:
I like a lot of salt on my popcorn, the oil/steam aren't enough for me.
The metal bar you can see in the picture spins around, moving the kernels. The top of the clear plastic cover has holes in it to allow steam to escape in ours.
You can't apply the salt with a salt shaker--too slow. Just use about a quarter handful of salt and distribute over the top of popcorn immediately when it has finished popping--I do pour the popcorn into the bowl first. Shake and the popcorn will be plenty salty. And yes, there is some residual salt in the bowl when the popcorn is all gone, but not a big deal--salt is plentiful and cheap. And you save a couple of hundred calories and some money from not using all that butter. But if calories or fat intake is not a concern, the butter is good. I just enjoy my popcorn without it.
Oh, and I just wipe out my Whirly Popper with a paper towel and stick it under the cabinet beside the stove. I wash it after every four or five uses or so.
I'm certainly not concerned with calories or fat.

Not only am I not extremely health-conscious, I'm about 5'9" and weigh about 150 lbs. And that is having put on weight in the past few years.
Don't get me wrong, I don't drench my popcorn in butter. I usually microwave some butter (margarine, actually) and pour it on right after popping. I sprinkle salt on from the shaker, use the top of the popcorn popper to cover the bowl with the popcorn in it, and shake it up. Then I'll use some butter flavored spray, add more salt, shake again. Depending on how much popcorn I've made, I might do that 3 or 4 times. I tend to make a lot of popcorn; I like large portions of my crunchy, dry snacks.
I don't care about the health of the bagged popcorns, but since my employer does, and has the popper, it's not too difficult for me to just use that.