In reply to sip a cup:
I think slopers are a better full arm workout than crimps but I don't think it'll hugely help with positive crimps.
When setting with slopers I've found you have to be a little more mindful of thinking about peoples body shapes: Positive holds let you get up really high on them with and hold them from a variety of positions yet sloper are much easier to hold when you are below them. This makes bunched slopers desperate for taller climbers who can't get their weight low enough while reaches above slopers can be very hard for shorter climbers. Also sit starts on slopers are frequently a real pain for the tall!