These are easily mass produced, and can be had for generally less expense. The strands are bound together by tight serving on either end.
The main advantages of these strings are that they come in clearly delineated increments of length and are usually less expensive.
Simplicity and low cost comes at the expense of range of adjustment, though: the serving holding the ends together may start to come undone if not properly done, or if the string is twisted too much and/or in the wrong direction.
As such, these strings are generally considered to be of a fixed length without any option for fine tuning.
In addition, the nylon serving that holds the ends together wears easily if there is any slight bur or edge to catch on, causing the string to fall apart.
Flemish twist strings are very popular among traditional archers. These usually cost a bit more, as they are typically hand made.
The strands of are separated into two or three clusters, then twisted and braided together to form a double or triple helix. The tighter the weave, the better the string.
In addition, more layers of string material can be woven into the loop section of the string.
This improves the durability of the loops significantly, and also bulks up narrow gauge strings. Due to the twisted nature of this type of string, it can be twisted and untwisted to a certain degree to fine-tune the brace height of your bow and find the best spot.
The downside is that these strings tend to have slightly greater mass, which will reduce the speed of the bow by a small amount.