The one in the pic is a biggie, it's the size I feed to my GS but it shows angell the whole thing. The springers will get one half that size with toe end and it will keep them happy as a chew when the weather's nice outside, don't be surprised if they dance around it before eating it, seems to be a strange ritual they have
Nutritional value wise I would think there's something in them, if they have one of these as a chew in the afternoon they won't get fed again that day as there is a bit of meat on them, skin and fat, well there's not much fat on them as it's a foot but I would say they break down as roughly 50% bone, 30% meat, 10% skin and gristle and 10% fat.
My butcher brings them whenever I ask for them but I only let them have about 1 a week, they are free as he would just throw them out. The French, apparently treat them as a delicacy, or so I was told when some posh bird came into the butcher shop one day and I was handed over a few, she said they like to boil or roast them up as they are very tasty, other than that I think some butchers use them in brawn or sausages

Some top chefs sell them in their restaurants and charge silly money for the dish too
A word of warning, if they have a trotter then the next day they will poop out little golden yellow nuggets so don't be alarmed at this! They are more bone than meat and are great teeth cleaners but I certainly wouldn't feed them everyday purely because of the amount of bone in them. I have also never seen any pieces of bone in their poop after they have ate a trotter, they seem to break down very well indeed, it's just the yellow colour poo they leave behind I find strange!
All the trotters I have are clean, same with the pigs ears but I run them under a tap and sometimes scrape out the ear wax if there's any

in this country when pigs are slaughtered they are dropped into scalding water afterwards to burn off the hairs on the skin, I think this applies to most places that kill pigs anyway, this will clean off the pigs skin too, watch out for ear tags left behind, I've had a couple of those left in before but they snip out easy enough.
The only incident I have ever had when feeding a trotter is when Zante got a piece of bone jammed in a back molar, it seemed to have stuck her teeth together and I only realised something was wrong when she went all quiet and I could see her mouth was slightly open and she just didn't look right, she must have been like this for half an hour or so before I noticed as she didn't make a fuss. I managed to prise the bone out and she was fine, pigs trotters have section like bones in them, think like the segments, joints in your fingers, they are rounded off and pretty hard but even my old girl Sophie can eat one and she's got a few teeth missing, given the choice though she prefers a pigs ear to chomp as it goes down quicker!