Shellac is good for filling the grain prior to putting an oil varnish on as a top coat (you don't want ANY shellac left standing on the surface of the wood). This finish leaves the wood clear and bright and the curl is brilliant.
Shellac is EXTREMELY abrasion-resistant, but it is also hard and brittle. Not a problem when just filling pores, but it can be a problem as a top coat. I've never attempted to do a top coat of spirit varnish. Just filling grain is fairly easy. Slop it on, wipe it off. OK, it's not THAT easy, but there's not much to it.
I've been using Button lac, which has been working well for me. I think in my last batch, I even added some mastic, which, theoretically, aids in making it more elastic. If I remember correctly, the order of refinement is as follows: seedlac (raw), buttonlac, rubylac, shellac. Shellac is further refined into garnet, orange, and blonde colors.