They are a good high pressure pump, and Airtex did make and may still make pumps for Merc. Only difference is the black paint. As for OSO, it all depends on who you talk to. If you get the 650+ HP guys, they only want Weldon, Aermotive and maybe one more.
Have to remember OSO is mostly high dollar boys and their toys. Most the other guys just let them talk and only comment when there is a need