There's a guy in Australia making sway bars, I know one owner swears by his mod, he chose a 24mm front sway bar which apparently improves handling and reduces understeer. The factory spec is 30mm, which is quite stiff already. The 24mm is softer and brings the front/rear ratio closer to the other MG4's, which are lauded for their handling. The company is called
Signature Sway Bars.
I'm interested in getting one, but a month ago I got my wheels realigned/balanced and the shop also installed camber pins, which allowed for a camber adjustment, and my handling and understeer is greatly improved.