There are various versions of the Mission arms, some highly respected. Mine is the budget one made by Jelco.
https://www.vinylengine.com/library/mission/774lc.shtml
Nothing special, EXCEPT, it has a very short rear counterweight section which I needed to add a 3rd arm on my TT within the dust cover when on. I use it for MONO cartridge ready to go.
Also, it is a small diameter base (very close to my JVC's TT’s wide rim); and easy mount. In my case, the base was threaded for 3 screws from below. I drilled those holes all the way thru and surface mounted in with 3 black wood screws.
Mine has a delayed drop when lowering the arm lift lever, an asset when using it backwards.
luckily for me, the seller knew how to measure properly and give me needed answers.