Currently training for a HM in the new year, and to date I've measured all my runs and my pace in KMs.
Wondering whether there's a benefit to switching my training mindset to miles, given the HM is traditionally an imperial distance, and will have mile markers rather than KM markers.
Any thoughts or opinions?
Yeah, this is my dilemma, really. I'm so used to KMs as they're part of my routine, and I've been increasing my long sunday runs in 1km increments, and I know where I am with that 1km extra, so if I switch up halfway through it might be an unnecessary mental burden.
Serious runners tend to use miles. At my club they always talk about min/mile pace rather than min/K when describing a proposed run group. Having said that, I much prefer to work in km because a kilometre passes faster and it gives me more split times on my watch. Remember that a HM isn't a set mile distance either. It's 13.1 miles or 21.1 km.
The way I think about a HM run in km is to think of it as 4 parkruns back to back. Then just when you get to where you expect the finish to be you find that they've moved it back a bit (think of that extra K as your "sprint to the line" distance...). I wouldn't worry about the distance markers as for a big event they will probably have both mile and K markers (Great North Run certainly does). For a small event the markers can be a bit of an afterthought anyway (I did one where one of the markers was sprayed onto a cow in an adjacent field - unfortunately no-one told the cow that it was supposed to stand still). I also find converting between K and miles to be a useful mental exercise when I'm running anyway. Otherwise, just learn the basic conversions off rote: 5K = 3miles, 8K = 5miles, 10K = 6 miles, 16K = 10 mles etc. It's not that difficult.
I don't think it's an issue at all. Don't worry about it! Kms is fine. It's the same distance fried or boiled, and that's the important bit to remember. Don't get diverted by stats. Focus!
You're burdening yourself with unnecessary anxiety! Chill out .......
I frequent another running forum -- whose main demographic seems to me to be young male Americans. Lots of testosterone flows there - and of course they all talk in miles. I am certain that I have noticed how the use of miles instead of Klms has influenced the way that they train. As an example, the distances that they quote that a runner "should" be running each week ( when converted into KLMs) seem to be extra-ordinarily large to me, even taking into account their youth and competitiveness. 30 miles is almost 50 klms - and they often quote 30 miles as a minimum weekly running volume for training for a 5K. 
Yeah, I've learned to avoid most "serious" running forums because of that attitude. I doubt whether most of them are even doing what they say they do
30 miles per week training for a 5k? Yeah, if you're Mo Farah 
Go on a continental 'serious' runners forum, they use km 😉
I did use to run in km but for HM training and onwards, I've gone back to miles. I appreciate that running km splits will be quicker but for some unexplained reason, I found that counting up to 21 felt much harder than 13. Odd but feels easier to run 10 miles rather than 16k!
I made the switch to miles when I started my HM training. It is easier and easy to work out a 5k (3.1) and 10k (3.2) and so on!!!
Good luck with your training...
Runners world training plan
Ekkk - 8 miles tomorrow
