I swear I had this all written in my mind. Then, after pedaling through the tunnel on my commute home, I happened upon the happiest and speediest three-legged dog I'd ever seen. Total ripper. Yes, sorry, no photos. So. Damn. Cute.
Anyway, after witnessing three-legged lightning, I was sort of over being grumpy about proper shitty tool-free brake lever adjustments. You know the ones. They would be significantly better if they just required you to use a hex key for adjustments. And, of course, provided proper access to the tool.
How often do folks adjust their lever reach? I think the Hayes Dominion A4 has the best take on the concept out there both in terms of integration and function. But, I'd still take the cleaner look of the T4 system's carbon blade, and tooled adjustment, if it weren't for the fact that reviewers often can't be choosers.
Regardless of whether you love a nice tool-free reach adjuster or would prefer to just use a hex key as needed, I think we can all agree that either choice is absolutely superior to a crappy tool-free setup. The worst part is that you know you've paid more for the said shitty system than you would have to just insert a 2mm and turn.
A case in point is TRP's Slate T4 brake system. Not a standout in any regard this four-piston system is approximately competitive with a SRAM Guide or G2 brake in terms of power and has a similar lever feel but uses mineral oil as the hydraulic media instead of DOT fluid. I think they're a very decent choice for the price of entry, but anyone who can spring the extra cash for a Magura MT5* or even Code R setup would be very well suited to do so.
*For riders with smaller hands, be certain to get the HC lever blades.
So it's not that the Slate isn't a very usable brake system. The lever feel is good both in a tactile and an engagement sense. They're quite serviceable and relatively easy to bleed even. But while the power is 'meh' the reach adjuster is awful. It's ugly, it doesn't turn nicely, and it's uncomfortable to use.
There are absolutely less-usable tool-free systems. Take, for example, the very minimalist knurled end on Formula's Cura levers. The difference is that everyone with Cura brakes just adjusts them with a hex key anyway. Not an option with the TRP.
Magura and Shimano both sell brakes with very usable tool-free reach adjusters. Little plastic knobs that are easy to turn. But in both cases, the tool-required versions of the brakes look much better. On the Shimano front, check out a Deore M6120 master cylinder versus the more expensive options. Even with most of their premium models, Magura has retired the tool-free adjuster in favour of their clean, quick, and easy 3mm hex grub screw. My guess is the next generation of the MT8 and MT7 Pro brakes will follow suit.
And that was pedaling the long way home to say that the tool-free lever reach adjustment on the TRP (Tektro Racing Products) Slate brake sucks. If you're not going to do it right then don't do it, especially since it's not an adjustment that needs to be made regularly and a tool-required option would cost less.
But if you are going to make a tool-free lever reach adjustment at least make it good. See Shimano, Magura, SRAM, Hope, and Hayes for how that's done.