While the "mini" in their name might suggest something very small, these are in fact very close to being "standard size" tuners. The difference between them and standard M6 tuners is not so great that you would notice immediately, but when installing them on a custom Telecaster headstock, you certainly will - those few millimeters of size reduction actually make the final installation much neater (and, likewise, they are also very neat on a strat-style headstock).
As with all Schaller products, the quality is second to none. The turning action is smooth, the ratio high enough to allow precision tuning, and the gears within hold the tuning fast, minimizing the frequency of retuning.
I have used these as an accompaniment to a locking trem and they are perfect (the locking version of these tuners with a locking trem isn't a terrible idea, but is not essential; using these also saves a little bit of money for other gear, which is never a bad thing).
Fitting them is straightforward, and they remain solid on the headstock once fitted. And while black hardware can seem "all the same", the quality of these tuners is actually apparent to the eye as well as to the touch. Highly recommended.