Is chemical stripping as good as bead-blasting to prepare a steel frame for repainting?
Both processes serve to remove paint coat from your frame. The only difference is that bead blasting may (or may not, depending on the medium used) scratch/damage the metal surface of your frame.

If you don't like that possibility, then you can opt for chemical stripping (especially if they'll treat the frame after for effective coat adhesion), but I'd consult with the establishment first on how your steel frame would react to the chemicals.

With that said, the link you gave also advertised giving treatment to your frame to prevent under-coat corrosion, so that's a nice touch for me.