I'm reloading for 45 Colt and 44 Mag. How do the Redding Profile crimp and the RCBS roll crimp dies differ? I've got the RCBS dies. Thanks.

The Redding profile crimp also has a taper crimp that leads to the roll crimp. This lets you get a stronger crimp without the crimp causing the case to bulge just below the crimp.
A good crimp is nice, but you really need good neck tension to hold the bullet - if you can spin the bullet by hand after it is seated, but before it's crimped then you need more sizing or less expanding in the case neck area. The profile crimp die lets you keep that tight neck and still get a good roll-over crimp. You do have to seat the bullet in a seperate operation using the profile crimp dies.

Some of the best money you will ever spend in reloading is the Lee Factory Crimping Die. You will never use the Redding or RCBS feature again after you get a Lee.