My two get them - a small mug twice a day. They compliment the feed I give - which is Simple System Chaffs as they are high in protein and oil.
Mine now have rock hard feet that rarely chip and this effect has been seen on three of my horses over the past couple of years - all of which are not shoed.
They also darken the coat and give it a very good shine. They need to be fed for about a month for the coat to change and the feet take six months or so as the new horn comes through.
I just put them in the feed and mix in. A few do escape and this year I had a few nice sunflowers on the muckheap but the majority get chewed up and digested.
There are sunflower oils far cheaper in supermarkets and that's basically all you're offering if you give whole seeds to your horse. There's not much oil in a kilo of seeds, either.
I sell them, as it happens, at £16.50 for 20kg. There are also plain sunflower hearts (shelled version, better value) at about £30 for 20kg. But I don't feed either - they're just for the chickens and wild birds in my opinion.
I had the same problem with tiger oats - pay a premium for these "balck oats" and ended up with them growing on my muck heap!! I used the sunflower seeds for a good 6 months but there was no difference at all in feet etc although my horses were in fab condition already! I just wanted a source of slow release fuel for stamina which was non-heating and not straight oil, the outshine has done the trick!
I actually started using outshine instead of the sunflower seeds, I had resisted becasue of the price but once i realised the hearts were the way to go decided to go for the outshine which did the job properly! (also used instant linseed for another horse with good results - although put her on the outshine eventually too)
Looks like Theresa_F and I are the only ones who like them! I think they are fab. My horses get a small mug once a day. Their hooves are fabulous (farrier who never passes comments is in awe of the quality of my retired and shoe-less 17.3hh gelding's feet) and both their coats are fabulous. I have never had any problems with either of them keeping weight on since feeding them. Last winter was their first full winter on them, this winter I am feeding them considerably less and they are both doing the same work.
I think they are wonderful and dont find them in the poo or sprouting in my muck heap! I buy them from Countrywide.