As a coach for some 10 years, I used Promatic and Acorn a lot.
The former was arguably the better of the two but they were all old traps made very well and worked beautifully.
A word of caution: manual traps are dangerous; self cocking auto traps are even more so. Be VERY careful and always treat them as you would a gun: loaded until proved otherwise.
I have seen some horrible injuries resulting from poor safety with auto traps from mangled fingers to broken jaws.
You simply can not be too careful.