Steve is right, and by the way, we've just discussed that recently in this thread...
http://www.subsim.com/radioroom/showthread.php?t=185585
... where I pointed out that OM + TMO gives you some problems with traffic and targets, if you try using OM for anything different than playing german subs in german patrols.
'I'm going down' said this when I made this remark...
"I do not know what you are talking about. Other than the difference in setting up the Aob, which takes some figuring, and using the wheel in KIUB, the games seem to me to be very similar. I have played TMO, FOTRS, RFB, GFO. stock with OTC, and OM/OMEGU/KIUB."
... but I stick to what my experience dictates: OM is great as a stand-alone supermod. Mixing it with other mods - specially when trying to play again in the american side - gives you mod-soup-headaches of several sorts.