I have a Ryobi 40 volt string trimmer and it eats the factory string like crazy or it vibration welds the string together in side the hub. I bought some after market string made by Ugly Line which was better, but still got used up quickly. I just purchased and tried some string from Maxpower and it is much better than any other I've used. With factory string I would have to reload the reel about twice per battery charge (about 30 minutes of use). With the Maxpower sting, I can trim the entire yard twice with a single reel of string (about 3 battery charges).
While reading the manual to see what size strings are correct for my trimmer, I ran across a note that suggested spraying silicone onto the string for better feeding. So far I've not had one incidence of vibration welding inside the reel since I started doing this.