So I didn't know this, but by using the bonus to optimal mass for shields from some of the engineering blueprints it is possible to fit a grade 5 shield to a cutter. Not tried it yet as I'm on the other side of the galaxy, but will certainly give it a go on my trade cutter when I get back.
Full explanation given in this thread over on the FD forum.
I'm guessing it can be applied to other ships/builds as well