Personally, I am a proponent of upping your training before you up your bit (I had a stopping issue with my horse when we first started riding together in a double jointed snaffle-- it was tough, but now people are impressed with his responsiveness!). That being said, both of the 4H girls at my barn ride their mounts in kimberwickes when they are in English tack-- one of the horses is a former barrel horse who has lots of get-up-and-gogogogogo.
Haflingers are cute stubborn little things. If I were in your shoes, I might see how he goes in a Kimberwicke while looking into a trainer for a long-term solution! Or, if you can-- get on him and school him yourself. There are tons of tutorials and suggestions online for putting a good stop on a horse.
Sorry you've had a rough experience on the forum. Everyone has a different way of providing "constructive criticism!"