Anyone tried Cycling ‘arm warmers’ for hiking?

Yes. It works really well, just roll them down to the cuffs of your wrists when you get warm, roll them up when you get cool. Arm warmers function as my winter "longsleeve top" with my summer weight wool T-shirts- it works for trail running, no reason it wouldn't work for backpacking. The Smartwool armsleeves in black are inexpensive and comfortable…warm too. I don't know why more people don't do it in mild weather. The only issue is the weight, they're a touch heavier than some lightweight merino hoodies, which offer quite a bit of versatility as well.

I think it's a great idea, go for it.

They also have sun sleeves that are high in UPF protection but not as heavy or hot as arm warmers. Pearl Izumi makes some.

I have a pair of Pearl Izumi wool warmers. They mate nicely to a vest or Montbell half sleeve down inner when needed. Very light and cheap (clearance at an outlet store).

+1 to added versatility in different conditions.

I use em to run/hike in all the time. Craft makes some very light ones with a uv block built in. I think they are on sale on this web site at the moment.

I've been using cycling leg warmers. Makes it easier on those days when you have big temperature swings. When it starts warming up, I can zip off my pants. When it warms up more, I lose the leg warmers.

DeFeet also makes good wool arm warmers and Pearl Izumi makes Sun Sleeves for sun protection. Both can be paired with a wool t-shirt (depending on weather) for a really versatile clothing system.

I think someone mentioned this above, but you can pull them down over your hands for warmth, pull the top cuff down on the upper arm if a little hot, and they let a little air in to the arms even if worn all the way under a shirt's sleeve.