I do not understand why we get Litecoins after the swap ? If i wanted to swap bitcoins, i should get bitcoins in the end. If i get litecoins, i will have to then exchange them for bitcoins at the exchange and it will involve tx and trading fee. This service is only useful if you want to convert your bitcoins to litecoins and no intention of converting back to bitcoins.
As you can see on their platform they are some kind of hybrid between an exchange and a crypto mixing service: "SwapMixer is a privacy focused instant cryptocurrency exchange. Unlike traditional exchanges, our reserves are used to complete transactions instantly and all data is destroyed at the end of a session."
Also they do mention that they'll add more altcoins after feedback is received from the users. However I'm curious if they plan to add two-way conversions, so we can exchange LTC to BTC for example.
This idea of having an "Hybrid" mixer is good along with the idea of adding more altcoins too, but they should also give the option to bitcoin to bitcoin mixer so that those who need bitcoin at the end of the transcation can also benefit from this service.