Just the rear will give a noticeable improvement but depending on bar and setting can make the rear a little lively depending on how hard the car is sprung,
I had the H&R 28/24 set on my ed30 briefly but found it a little too much in terms of ride comfort and the tendency for the car to skip around on a typical wet bumpy B road if driving fast..
Swapped to the H&R 26/22 with the front set on soft and the rear on hard (I prefer the car to have a playful rear end) and imo it's perfect for a fast road setup without sacrificing too much ride comfort etc, I should add I had them paired with OE dampers and -20mm VWR springs so the stiffer bars with a relatively softly sprung car made wet weather progress a lot less twitchy compared to the 28/24 bars

Front and rear bars are a great value mod imo, probably the best handling upgrade I did and one which I'm transferring onto the mk6 when I get some spare time
