$45 is a deal considering what the factory single row (non A/C) pulley will cost you these days. ~ four yrs. ago I bought a new one from Porsche for around $70. And I thought that was ridiculous. Now Pelican says they cost $120-something!!!
I think SR's main reason for offering it is to be able to use a distributorless ignition like Electromotive or Motec? Secondly is of course the removal of the unnecessary second row.
I don't think you save all that much rotating mass (less mass never hurts though- except for clutch/flywheel stuff), but why have the extra row when you don't need it? If I needed one today, i'd definitely buy the SR pulley. Looks like a good deal to me! And I bet it makes your car faster, soley based on the racy looking anodized alloy finish.........