A former colleague used to run regularly in them with his prescribed orthotics inside. His specialist said they were perfectly good trainers, very 'neutral' so good for orthotics or those with a neutral running style. His only stipulation was that you shouldn't do more than 400 - 500 miles in them before replacing.
Theres nothing actually wrong with them, I think the stigma is more down to squaddies generally not liking what is issued. If the forces issues it it must be crap! Plus private purchase is usually more gucci (actually yeh Silver shadows look wa nk but that shouldnt matter you dont go running to pose, and they are not you're going-down-the-pub trainers like the only ones my mates have!) and sought-after.
I used to run in them regularly. You probably want to swap the insole for something better. Or just pop one of those big thick rubbery insoles under the ones they come with to help protect your feet a bit more. I got some (CUSH-N-STEP?) for a fiver, cheaper than your 30 quid sorbothane rip-offs. Then the silver shadows wore out, so now I run in a pair of my own.
I wouldnt buy them. But if you are issued them theyre not as terrible as everyone makes out.
A PTI recently said she swears by them and surely they are in the know about such things and get plenty of running in?
Silver Shadows are the mutt's nuts. A hell of a lot better than the white lace-up plimsolls I was issued with back in the dim days before the dark days, and miles better than the green combat slappers they started knocking out a few later. And what's wrong with going down the pub wearing them? They're probably "retro" by now...
Having said that I now run in a pair of Asics, when I'm not VOR.