We've A/B tested a slider against a textbox with plus and minus buttons (banking, on mobile) and the latter seemed to work better (as in fewer users cancelled the flow).
I'm not pretending this finding can be generalised, though.
Wonga.com was (briefly) a huge success story with their "two slider" interface. Perhaps because it made it easy to see how the output changed with the input.
We've A/B tested a slider against a textbox with plus and minus buttons (banking, on mobile) and the latter seemed to work better (as in fewer users cancelled the flow).
I'm not pretending this finding can be generalised, though.