I haven't used the Dark Time or Urzwerg, and the Beatstep isn't out yet, but I think the Beatstep is absolutely a great choice.
The Urzwerg and Darktime are both analog sequencers. This means that they have analog potentiometers, so the CV output is continuous; as you turn the knob, there is no break from one pitch to the next. Mind you one or the other may have the option of quantization to allow easy setting of specific notes, I believe in the Beatstep there will always be an audible pitch change from one note to the next.
The Urzwerg and the Darktime, I believe, do not have the reverse/random options that the beatstep has. They may have adjustable sequence length which Beatstep may not have.
The Urzwerg and Dark Time have more CV outs; the Beatstep only has one. So on the Beastep you will only control pitch OR filter on your Minibrute, not both simultaneously.
But the beatstep is only $100, and it's a really cool midi controller, and it has 16 memory spots for sequences, and it has user assignable scales... I myself have been looking for a simply sequencer much more basic than this for around $100.00, so I purchased the beatstep on preorder from $99 at sweetwater the first day it was announced.
Edit: I should add that I have a Minibrute, as well as a couple of older analog monosynths so I am looking at this purchase primarily as a CV sequencer.