I thought it was just a bit spongy at first. But it meant that there was still air in the line. Once it's all out, it should be really quite firm, like a normal brake lever. Turn the master cylinders upside down, back to front, and round and round, whilst pumping the lever to get all the air out. Also, take your rear caliper off the bike, and turn it upside down and around, because often the bubble is in the caliper itself.

Getting it properly bled took longer than I thought it would. I was using a syringe from the caliper upwards too, but it didn't get all the air out. Turning everything upside down did the trick. And once it's done properly, it's amazeballs!