If you have the 2015 North Bar as well, it should have a single front line safety system, which wasn't the case on 4 line North bars prior to that (If I'm not mistaken all 2014 and older 4-line North bars were on dual front lines). In terms of safety, there won't be much difference between a single front line vs the 5th line, so I wouldn't worry about it. 5th lines have the advantage of flagging your kite symmetrically, in other words as if your kite was secured on the beach, which is ideal in any emergency situation.
5th lines sometimes have the (rare) disadvantage of flagging your kite as pictured below. 5th lines can also wrap around your kite when you invert it for example.
As Matt says dual front line safety are not always flagging your kite out when activated, hence when the 5th line option was a greater safety alternative.
Apart from the Rebel, the 5th line isn't loaded on the other North kites, so has no impact on the flying characteristics of the kite.
Christian
