i do, but i just ride in it like its a loose ring baucher, i.e. i use the top cheekpiece slot as normal, but then place my reins on the main large ring. i think my initial idea was to use it as such as my horse doesnt respond well to fixed ring bits, but i thought that it would give me a tiny bit more poll pressure than my bog standard snaffle. i'm sure it doesnt but the thought that it may have seems to help! Like a placebo effect or similar, and yes - i am a nutter!
My sister used one on her pony for WH as it's permitted in novice classes and she did need a little bit more control. It did the job for a few shows but then I took it out as the mouthpiece was very thin and started to rub her (the pony's!!) mouth so she went back to the eggbutt. I know a lot of people use them for WH especially the novice classes. They are slightly stronger than the other permitted bits and if the pony goes well in a 3 ring it might be an idea to try one. I just found that the mouthpieces are quite thin so this can also make them stronger.
I use it on my welshie for jumping and hacking- it has a slightly more fixed action than her normal eggbut. Both are french link. It enables me to flex her more, keeping her head in a sensible place which in turn stops her zooming off with her neck set against me and the two of us ending up in a pulling contest!