Fast Flight longbow string made in the Flemish twist style.
Flemish Twist Strings use a braided method of creating the end loops and are often considered stronger than endless loop strings. Flemish is also more common with traditional bows both because of their higher draw weights because the construction method dates back much further than the endless loop style used mainly by Olympic bows.
Both styles will work well with both styles of bow.
One thing to watch for with Flemish strings is that because there is no serving used in the construction of the end loops there will be exposed ends showing in the string. This can look like the string is broken, however this is normal for flemish twist and nothing to worry about. Don't cut or tug on those bits. Enjoy the more natural look of the design.
To see how they are made, here is a great page by 3Rivers showing in detail.