Thought I'd update now it's finished
Test drove yesterday and the brakes are amazing. The bonus is that the stock master cylinder is fine and needs relatively low forces to get good braking (keeps the bug wife friendly too). The only reason I could think of to switch m/c would be brake balance but I don't know how mine is. I'm going to wait until the Subaru engine is in to get the correct ride height at the back (need more caster) and then re-assess.
Rich