Is it sequential? I thought it spread out the threads according to -b - t- -p numbers...I am sure it does spread out, then check sequentially. The other software is the modified vanity search and keyhunt.
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You talk about technical implementation, I was talking about the way how it works. Of course if you have 2 threads, work must be somehow divided, but the idea is to check each key from A to B. Then there is stride, where you do not check "each" key, but still you decide which ones should be tested. I bet you see the difference comparing for example to Kangaroo, where tests are random (where BTW I have also implemented stride, for WIF solving).
Using "stride" or "random" mode as a shortcut to finding a key is just a playing a lottery.
I did not check yet VanBitCracken, but as I briefly see it is not a piece of brand new software, just a modified/patched version of old programs. Hard to say as there are no sources.