I have been fishing for over 65 years...
Until recently, I had been using a fairly obscure copolymer line named Breakaway (of all names for a fishing line!) This line was manufactured in Brazil and distributed by both the Breakaway company (which sells tournament casting equipment) and by Cabella's. Unfortunately they stopped carrying this line and I have been searching for a replacement.
The line had all the qualties I like in a monofilament type fishing line. I have tried various replacements but, none could fill the bill - until I tried Kastking Copolymer.
The Kastking copolymer line lays on my reels beautfully, casts wonderfully, resists backlashes and tangles, and has a very thin diameter.
I used this line in 30 pound test on a private fishing boat off the San Diego Coast while fishing for dorado as well as bluefin and yellowfin tuna. I landed a large bull dorado as well as several 20-30 pound class bluefin and yellowfin. I would not hesitate to use it on larger fish. I used it on an Avet MXJ reel along with a braid backing. I have not tried straight Kastking in lieu of a fluorocarbon leader. If that works, it will certainly save me a big expense as well and make setting up my gear a lot easier.
The line has sold itself to me and I plan on using it in the tests in which it is available. I use 10, 15, 20, 25 and 30 pound test on my various reels in various fishing venues. Eventually all those test lines will be replaced with Kastking copolymer line. I just wish that this lne was also available in 40 and 50 pound test. Then I could use Kastking on all my reels.
My only complaint is that the spool is quite unusual and will not fit on my Berkely line winder. I will need to jury rig the winder because, I am not going to let a little thing like an unusual spool prevent me from using Kastking Copolymer.
BTW: the fact that Kastking Copolymer line is relatively inexpensive is a big bonus.