You could simply do the best of both worlds - pre-book your KLIA Express ticket online with a credit card, and get the RM100 return deal (head from KLIA to Sentral via Aerotrain, and back via Grab).
My point earlier was...if you're on a biz trip.... costs probably isn't that big of a concern to you. And I'd imagine convenience and fuss-free connectivity would be more important to you. That's why I was recommending, if you're on biz travel, to just take a Grab to your final destination. Point to point, and hassle free.