This model will be equivalent to a rocky (50 mm planar grinding plates).
Mazzer is a "brand" rather than a model, and it covers a range of grinder types and sizes, so "grind quality" cannot be compared, unless we nominate something in the mazzer range that will be similar in type. The closest will probably be the M Mini with 58 mm planar grinding plates. This means, depending on motor speed or geared revs, that the mini might deliver grinds more quickly (or not) due to the larger diameter of the grinding plates HOWEVER that doesnt necessarily mean the quality of the grinds is any "better" ie, if you set both the BB004 and an MM up side by side and use the same operator, same bag of beans and the same coffee machine, will there be any noticeable difference in the quality of the resulting brews (once you have set both grinders up to deliver the very best result it can, together with your best technique to suit)??? Probably not, that could be attributed to particle quality per se. Any differences in the two grinders would lie in other areas, what they are initially designed for, what is the "end use brief", and the opinion of any particular tester or end user.
Just note that the BB0040 *may* have a bit of slack in the locking pin (of the adjuster). We have addressed this in similar grinders in the past, by substituting or making up thicker pins that sit much more snug in the hole, and /or the adjuster itself *may* have larger steps between one setting and the next. If so it would compare closely with the rocky in that regard, although I've never found it a problem because I am able to vary my operator technique slightly to suit (ie if I think one step is a little fine but the next step is a little coarse), as any good operator should be able to.....but it does seem to bother some operators trying to run with a uniform coffee making technique despite all the ever changing variables involved in the black art of coffee making.
After that you need to decide whether you want a "doser" or "on demand" type of grinder, what your budget is, and whether you can see any value in spending more on something else.
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