Having to transfer anyway, I really don't see the problem here bar the lack of being able to utilise the silver card that must be a bit annoying.
At half the price (I'd say it was a 50% saving whilst BA were 100% more in that debate!) and with a transfer at AMS as opposed to inter terminal at LHR, without the BAEC implications, any other decision than KL, would be madness
The savings will by you something far nicer in AMS than you can get in the Club lounge at LHR too, so basically it's only the double miles you're missing out on