I used one last year as my mare was a proper handful coming in from the field and kept rearing. To be honest it is quite thin and seemed to wind her up more she responded better to using the rope of her headcollar. Someone else at my yard however uses one for their cob and find it really works so I guess it depends how sensitive your horse is. Haven't had to use anything this year touch wood
I got mine at Charlies in Welshpool although haven't used it yet. Saw them on ebay recently at £15 - which they're so not worth TBH, I only paid a fiver for mine which is a fair price for a bit of cord (just a bit thinner than normal blue towing rope), two clips and a slide ring which is why I thought it would be worth a go; I think the clips are quite flimsy, might have to change those.
The new ones are better, made in England and using solid brass fittings you can get them directly from www.kempcontroller.com it also tells you how and why they work
I wouldnt be without mine! My horse used to bugger off in a chifney but with a kemp you can turn them on a sixpence and with her being 16.3 chestnut mare irish draft this is the only thing i would use
I found the Kemp controller brilliant. My current youngster youst to be quite bolshy and rear occasionally, after a few weeks of using the kemp controller to lead him etc he stopped all this behaviour and is as gentle as a lamb now. I wanted to nip his behaviour in the bud asap as Im on a livery yard whereby whoever is up first brings all horses in etc so I wanted him to be good to handle by anyone.
I have used it with a lot of horses and its worked for me.