I used to have a hot-rails many years ago in the bridge of a strat.
From my experience since, I would say that it sounded like a "humbuckerised strat pickup", not a humbucker - but memory might be playing tricks on me..
I got rid of it because, for me, it didn't sound enough like a strat anymore.
My gut feeling, on that experience, is that stacked singles sound fine if you want the sound, but they are neither "fish nor foul" when comparing them to singles or humbuckers... (I suspect that might be part of why Tim doesn't do them?)
I haven't heard Sinners, but everything I've read suggests that's the route I'd go if wanted to try the same thing again.