If you can figure something out of data published, here is the link http://www.ortofon.com/om-series-p-550
Beside small differences in internal inductance and impedance, there are no big differences in OM line of cartridges. Of course, OM 20 has a nude stylus, in its time it was well regarded cartridge. Comparable to 2M blue today. I tried to find one for my old Philips turntable but it is to difficult these days. So I ended up with 2M Red.
The majority of opinions regarding Invicta is that they are "hit or miss" as goes their build quality .
If so, I would avoid it. There are many other brands that are reliable and good. I personally like Seiko, all of their lines, quatrz or mechanical. Of course it has to look decently good.
Also, I do not wear wrist watch every day. But when I do it is because I need to check up the time quickly. A few years I relied on cell phones, but I get annoyed with how much time and movements I have to make just to check the time.
And for cheap and reliable, when I do not have to care what will happen if I hit something with my watch, I have Q&Q. Got it new for peanuts, they have reliable Citizen quartz mechanism, made in Japan and the do just well. In a Seiko I the battery last a few years and the battery in Q&Q lasts for one year more or less. So what.
Subscribe to the Dwight Schrute philosophy: When I die. I want to be frozen. And if they have to freeze me in pieces, so be it. I will wake up stronger than ever, because I will have used that time, to figure out exactly why I died. And what moves I could have used to defend myself better now that I know what hold he had me in.