Test accessories? They come with all the same stuff the production model does (no more, no less).
The 10 dollar premium you're paying for is going to basically be the custom shields and getting them sooner. The drivers and fit will be tuned to be the same as the production model as well. All physical aspects of the headphones will be the same as the production model.
Sounds like a sweet deal right? For the most part, it really is. You do have to note that this isn't technically a first batch, it's a pre-first batch (batch 0). That said, this batch is the set that will have any flaws in it if they exist. Most of the time, this batch runs perfectly and has no flaws in the design, build, etc. However, once in a blue moon, you'll find that the first few batches may have some bugs in them that cause problems down the line (couldn't be tested for). This is extremely rare, but does happen. If it does, since you paid, you should have a warranty that would be honored.
This is not "batch 0".
This is simply the very first batch of headphones to be made and checked after locking in the design - which, by the way, is done by listening through and testing all the headphones from "batch 0." as Val has stated before, these are part of the first production run - effectively part of the MPU units. These will simply be sold and given out 2 - 4 weeks before the full release of the headphone. What's more, is that these get personally checked by Val and his team, and are used to make sure the full release is ready and there are no big variances. In essence, these will be the best version of the M-100, baring a large-scale revision in the distant future.
I'm just glad I got an order in for one.