My original post was probably worded a little stronger than I intended and I meant my point to be a little more open ended. I don't specialize in either kattara or Manding weaponry so I wouldn't feel comfortable trying to seriously argue it either way. But just for the sake of discussion... There is plenty of documentation of Arab traders, settlements even within the larger Sahel cities of Arab merchants so all the pieces are there for it to be Omani influence. My issue is that in these regions literally everyone was using some variant of these trade blades, kaskara, takouba etc. This exact blade style was manufactured heavily in the Hausa states much closer to the Manding areas. The style of hilt on kattara is pretty simple and the Manding swords are a bit different in the pommel terminus, a element which shows up on other Manding weapons with slightly different hilt variations such as this example:http://oriental-arms.com/photos.php?id=2462
I've also personally never seen a wire covered hilt on a Manding sword which I thought was pretty distinctive of Omani katarra (please do correct that assumption if I'm wrong!) I'm not saying there isn't influence, just that personally I'm undecided as the form is simple enough in my opinion to not necessarily need influence to explain it. It is after all just a grip with a somewhat decorative terminal. I have a tendency to wonder if we, generally speaking, aren't too quick to try and connect a lot of forms which could just as easily be explained by local innovation. Of course this is somewhat playing the other side for the sake of argument. :-)
Interesting that you mention the point that the style could of transmitted from the mainland to Zanzibar and then Oman - that would be opposite direction I'd expect. The Manding do seem to have picked bits and pieces from all over the places - I've got a takouba that's Manding as well. Either way an interesting topic to be sure.
Not wanting to take this thread offtopic I'll PM you with a few questions about the wide blade Omani form as this situation mirrors two takouba types.