December 2018 update on this property... The rate is still listed as being at 4.36% over Visa's. I was offered a charge of $336.23 via DCC on a bill of NT$9900. The posted transaction was $321.41, saving $14.82, effectively a 4.61% surcharge. I don't know where they get their percentage markups because they've never been accurate even when taking into account exchange rate fluctuations. I ticked the NTD box and signed the slip with the DCC verbiage - and was sure to take a photo before the lady took it away - and presented with a final DCC free credit card charge slip in NTD.

I'm in Singapore now and have been able to avoid seeing DCC via Google Pay use (plus taking advantage of the promo with Chase).