A machine like Rancilio Silvia requires a great grinder before your espresso really starts coming together. It's possible to struggle along with something like a Solis Maestro (been there done that), but you gotta have a genuine full-time espresso grinder for Silvia to really shine.
Macap's M4 is a full-on espresso grinder, suitable for light-duty commercial work (and Macap makes bigger ones too). As you'd expect, it's solid, and well-constructed from quality materials. It has a physical presence that pictures don't carry across - standing on my coffee bar, it makes my Silvia look like a replacement machine while my "real" machine is in the shop! Even my wife pointed out that the Macap M4 outshines the Silvia's physical appearance and has even suggested an upgrade.
People tend to compare this grinder to Mazzer Mini, because they (once) shared a price point, are similarly sized, etc. Besides the functional differences, let's just say that M4 has a better doser design, easy grind adjustment, and the power cord's in the right place =) The M4's appearance is closer retro-chrome than Mazzer's sleek modern Italiostyle, so it fits right in next to the Quick Mill/Isomac styling.
M4's grind is superb. Extremely even, consistent and beautiful. There's no point critiquing it, it's on the same par as Mazzer Mini's. It goes from empty to grinding with no apparent change in load on the motor. Grinding is slow, however. 30 seconds or so per shot can feel like a long time if you've got a lot of espresso to make. For the home barista, though, this is a blessing in disguise. It's very hard to grind too much coffee by leaving it on a touch too long.
The doser is great. There's a fairly short chute between burrs and doser (a typical request from Mini & Rocky owners), and the veins are designed to sweep the container clean. Many people comment on the doser fork, which is very solid and sits close to the doser bottom. The doser handle is solidly designed and the action is very smooth. At first glance, the tamper attached to the doser seems corny. But in fact it's very solidly made and dependable for dosing and leveling. Fits a 58mm basket.
Only gripe is the catch pan. It's not really big enough to catch all the grounds (which can fly far to the left if dosed vigorously), and you need to lift or tip the grinder back in order to move & replace the catch pan. Small quibble though.
The quality of shots from a Silvia & M4 is extremely high compared to a Rocky. I'm not a particularly good barista, and I'm even drinking my bad shots now. They're rich and full of flavorful coffee oils, and the texture is far improved.
Now, step vs. stepless - I was suprised to find, after unpacking, that I'd been shipped a stepped model. Espresso grinders in today's day and age should be stepless, or have extremely small steps. I've gotten used to the stepped M4 though; my tamp isn't set in stone anyway, and insisting only on a stepless grinder seems a little too alt.coffee fussy to me. If you slightly adjust your tamp & dosing, you won't need a stepless grinder at all and will be making ristrettos in no time, so don't fret if a stepless model isn't available to you.