Sensitivity
Both the Berkley X5 and X9 braid comes tightly wound and have almost close to zero stretch. This makes allows them to transmit vibrations well which means that they are super sensitive allowing the angler to feel every bump, surface, etc. Apart from this, having almost zero stretch also helps the angler set hooks more effectively amounting to more hook-ups.
Good Knot Holding Strength
Ok, before I go on to talk about knot strength, know this. Not all knots are suitable with braided lines (or super-lines). This is because braided lines (super-lines) can dig into each other and cut each other. Four knots that I recommend are the Berkley Braid knot, Uni knot (with more turns- at least 10 turns or loops), Palomar knot, and improved San Diego Jam knot.
That said, smooth lines are usually slippery and knots may not hold well. However, Berkley super-lines including the X5 and X9 Braid holds very well. Perhaps it is the coating used. None of us have experienced knots slipping during the months that we have been using them. Most of the time I use the Palomar Knot as it is the quickest and easiest to tie. So for, I have not had any knot slip as well despite it being a simple knot.
Good Lines Great Price
While the Berkley X5 and X9 are not cheap lines; they are quality lines at more affordable price points. They certainly are good value for money for good performance lines that provides for good distance casting, good sensitivity, better strength and toughness, and good knot holding strength.