I love these arm warmers! I get hot quickly on my runs so when I am on the track, I can just throw them and pick them up when I’m done. They are small enough to put them in your pocket if you are out on the roads.
For races, I just use dollar store socks from which I cut the toes off and throw them away once I am warm enough, but for my training, I really like the softness of the material and the comfort of a nice pair of arm warmers.
They are much easier to take off than a long-sleeve shirt and they give you nearly the same warmth. Especially if you have your headphones on, you will appreciate not having to bother with taking a long-sleeve shirt off. Not to mention if you have your phone in an armbend! So it is a simple and very useful accessory to have on those colder training days.