Did you mean PureMixer service fee is among the lowest on the market? I don't intend to promote whirlwind in my post but they offer free mixing and that's donation based as we have seen with ChipMixer. Although whirlwind is doing this as an experiment for the next 3 months.
PureMixer code can ensure that any user won't be receiving his BTC accidentally. That's great. I'm not really an expert here but what will you record here? Say my PureMixer code is- ABCDEF

So, whenever I will put this code, you will ensure me that any previous tx from me won't be sent to me. So, you are recording all of my bitcoin send/receive address under the PureMixer code ABCDEF? Am I right? So, you may not have any clue who am I but you will surely know a lot of my addresses, I mean ABCDEF owns all these addresses. Can you please explain it more because I'm not an expert here as I said?