Yes. I do. Not for any aero gain (no idea if they do, and lower leg skin drag is SOOOO low down the list of aeas for improvements to my race time anyway) but have them for the run.
I used to think they were snake oil, until some calf problems. Started using when in desperation to try anything and seemed (utterly unscientifically) to help with reducing the re-occurance of a repeat calf strain (I have a lot of deep scarring in one calf from an accident when I was young). The benefit could be in my head of course.
As all my tri have been wetsuit legal then I put them on under the wetsuit before the swim and then they stay on all day.
(Also 2 or 3 long tri have been in bad weather so the extra layer helped there anyway).
I’ve raced with them due to the aero advantages (if they have the right texture). I’m 45s+ faster over 40k with them than without. Personally, I hate running in them, and will take them off in T2 for 70.3+ races.
I bought some aero calf sleeves (so non-compression, just thin ribbed lycra) at the end of 2019, but haven’t had a chance to race in them due to Covid. My hope is that they are even more aero, and more comfortable to run in.
The compression sleeves (18-25mmHg) have been really helpful for post-race recovery, and for dealing with shin splints.
There are two different products here that need to be distinguished. Aero calf guards, which are only intended for speed and do not pretend to provide any recovery/medical benefit). Notably made by Rule28, Aerocoach, Velotec, etc. These seem to be objectively faster than shaved legs, to a significant degree. I agree it’s a mistake that more pros don’t race in them, but I’m not complaining there. Note that you can’t race in them unless it’s wetsuit legal (unless you put them on in t1 which would take awhile).
Then there are compression sleeves that supposedly help blood flow. I’m aware of CEP making some, and I’m sure there are other companies out there. No claims of being faster, though some people like the feel and could be as much placebo during a race as anything, which doesn’t mean they don’t help!
While my aero calf guards fit snug, they are not nearly compression sleeve tight. I’d imagine maintaining aero properties would be tough while also making something thick and tight enough to get the body benefit side of it.