SWAP.BTC is centrally issued and controlled. You have to trust the deposits will not get stolen by the provider and will behave correctly. In fact a hack occurred stealing 10s of thousands of dollars happened a few years back resulting in BTC lost. This poses a significant risk to anyone using SWAP.BTC and treating as safe as normal HIVE or native BTC.
SPK aims to build a swapping layer that is fully decentralized and trustless retaining a high level of security through smart contracts and other mechanisms. More details will be released at hivefest in Sept.