This is 12-28. If you go for a 12-30 you may need to change the rear derailleur cage as well. Check it.

My new road bike came fitted with a Ultegra RD-6700 SS short cage rear derailleur and a 12-28T Tiagra CS-4600 cassette. I swopped this for a 12-30T cassette. My bike is a 2013 model and the outer guide pulley cage, by the top jockey wheel is stamped 30T, contrary to what the Shimano documentation states about 28T being the largest sprocket recommended. I suggest you check yours. You need to adjust the B Tension screw in (clockwise) to get the top guide pulley wheel to clear the bigger 30T sprocket, otherwise when you try and shift into the 27T, 30T sprockets the derailleur will foul (overlap) and jam the transmission leading to expensive damage.

I use this cassette with my spare set of wheels for mountain climbing. My bike has a Ultegra di2 groupset with compact cranks My lbs where I bought my bike said it would work fine and it works perfectly. Shimano tend to be a bit conservative in their rds ability to engage larger cassettes. Anyway these cassettes are such great value that they are worth a try.