No need for extra charge to use LTE. If you are using the old sim card, just go to the center and ask them for the 4G Micro Sim, and you're good to go.

Personally I use LTE everyday. and its hard going back to 3G/H+ and its quite stable too. I work in Masjid Jamek, and lives in Jelatek. Weird thing is, KLCC doesnt get LTE. hahaha. I'm using Maxis, which ironically maxis HQ is there. Gagagagaga...

I'd say if you live in KL, LTE is gonna be worth it. The coverage and speed keeps on increasing everyday. Its been like 4 months since I use LTE here. It keeps getting better and could be available in new area in a few months.