It was my first real time on a treadmill and I cannot say that I am fan, yet. My daughter is. She is/was a gym-goer so very used to them. .
First thought? Not enough fresh air, the room (garage converted-ish) felt so warm/hot, even with no heating on and door leading to utility room and then to back garden open; I was drenched with sweat. My balance was a concern - it took a bit of getting used to the feeling of being 'forced/driven' to run if that makes sense?), at a constant pace and on a flat-bed. I am now used to road running, with its altering terrain, lumps and bumps that you naturally adjust for. The natural of control over slowing down or speeding up at will, when needed, is what I like, expect even.
The run itself ended up fine, though I'm dubious about the distance meter, but getting off the treadmill at the end, my head believed the floor was still moving beneath me, it was a little unnerving, somewhat nauseating even. I might get used it, might not, but in the main, it will be the good outdoors every time for me - I'll give it another go no doubt, when the weather is so bad, or we're not allowed to leave the house even, thanks to this dreadful virus (let's hope it does not come to that!).
Keep running all, and keep safe