Problem is, the more they are there the more we notice how their main conceit fails. Blink was fantastic, the urgency, the fear, the uncertainty and resolution all worked. But after that, their power only works when the writers want it to, leaving gaping holes in plot believability.
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Yep. I'd prefer they just get a spin-off show of their own to be honest, rather than shoe-horning them into Doctor Who episodes.