Bob (Litt),
I see all good answers so far. I think, however, you need to distinguish between two issues. First, your profile does not specify where you are from. Your place of residence has an impact on customs questions. From reading here and general experience, one small Sebenza is not generally going to be a customs problem from the standpoint of duty. If you are from the United States, carrying one knife made in the U.S. is not a customs duty issue.
This would be contrasted with taking a trip from the U.S. to Japan and returning with a new expensive camera. If purchased in the U.S. you better have a U.S. receipt or have registered it with Customs before you leave. This is provided as an example and used to be true. I assume their may still be a duty issue, but do not know. I remember taking a trip with a lot of camera equipment, and I registered it before I left.
Secondly, I believe you are more likely to be trying to ask regarding weapon issues, which is how the answers are generally phrased. As far as the FAA seems to be concerned, in the U.S. a small Sebenza is OK. Airlines, however, can use their discretion. Prior answers have already discussed this, such as the padded answer suggestion. It is also a good excuse to buy and Umfaan, even smaller and more innocuous.
Two problem points, from reading the forum posts, seem to be England airports and the chunnel. England is apparently more violent than one would normally suppose and thus lawmakers there have apparently frowned, at least in a general way, on locking folders. This is apparently true, no matter how small the locking folder, treating them as forbidden fixed blades. I wonder if a blunt, Spydercard or similar would count? I also recall reading of one person passing through England on the way back from Italy (?) to the U.S. with a fixed blade, purchased in Italy as a souvenir, and having it confiscated. I suppose they are worried that gangs of foreigners, especially Americans, are going to escape from the airports and cause a problem, or that if in checked luggage ,that a baggage handler, or official might be tempted to take it thus introducing it to England. So if you have firmly fixed in your mind, a picnic in the bucolic English countryside, you may need to be careful in choosing your picnic implements.
At 2 7/8," blade length is probably not usually a problem, but there may be exceptions. A small Sebenza would generally not have serrations, so that would not be an issue.
I also wonder if the Leatherman Wave and similar tools would be frowned on because the blades lock. This might be a good use for that old model, original Leatherman tool.
I also read a post in one of the forums regarding the chunnel. They are apparently extremely afraid that someone is going to hijack the train, going through the tunnel between England and France, or have some other concern. ?? Further, there is no provision for checking ones luggage. In any event the post suggested that they forbid ALL knives. I hope that has changed, but that was the most extreme example of which I have read. I wonder if they would overlook a waiters corkscrew?