I don’t remember seeing anything about extensions…I will have a look around the blog to see if I can find anything.
The sliding battery cover is just that. No need to unscrew anything, it slides sideways instead.
In terms of the lower sampling rate… I will try and find where Seeed explicitly said this, but the recent blog post they made about overclocking the Analogue to digital converter discusses a 2 channel device… ergo the sampling is being done through different hardware and hence will likely have a different sampling rate
The specs say 30S/s – 72MS/s so I deduce that the 30S/s is the digital channels, the 72MS/s is definately analog.
I thought you were getting a Quad Ben?