The kneffy twister is the best thing to happen to top string. Knex -
https://www.knex.com/parts-extras - had a deal where you get $5 off your first order. When I placed my order back in February, the total was only $10.89.
A whole new world opens up when you twist your own string. You can make whatever diameter or length you want, not to mention color combos. You can have a lot of fun with the string buttons, too. I've used everything from my zoo membership card, to guitar picks, to wooden buttons, or cut up plastic lids.
The best part is discovering which string works best for you on each top. I like a six ply on my lightweight tops, like a Duncan Imperial. On a heavier, but still small top, like a Cometa King Turbo, I use 8 ply. But, the most surprising thing for me was that I really like a thicker string on my Spintastics QuickSilver, so I use 12 ply.