The normal plastic TL01 steering arms give toe-in, which is good for stability, but make the car understeer. These adjustable arms allow you to run toe-out for drift and grip driving, and to recover toe lost by lowering your car. I recommend 1deg toe-out for drift setup, and 2deg toe-out grip setup. My only complaint about these turnbuckles is that you don't get a very good surface to grab on to for adjustment.
No TL-01 can be without one of these. If you want your TL-01 to drive properly, do yourself a favour. Buy one of these. It allows you to set the trim of your steering more accurately, the plastic steering arm just doesn't work, don't even bother using them. Just get these Turnbuckle. You'll be glad you've got them.