We are thinking about adding ChipMixerLite version that would work exactly like old BitMixer - you send output addresses, receive signed contract, send coins and wait a few hours to get them. The good part would be simplicity. The bad part would be split of mixers volume and less privacy. What do you think about it?
Honestly i don't think it's a good idea.
Chipmixer is a brand by itself and is the first to use private keys directly as a mixing tool to achieve 100% anonymity. Having a chipmixerlite will only confuse users, and probably create a split between the pathways to take which is not good.
I would consider adding a minimum fee instead of donation because as you said a lot of people from Bitmixer are used to having a mandatory fee charged alongside with their mixing process. After all you do need to pay for the transaction fees when you transfer funds into individual chips, pay for server, support, and advertising costs.
Personally, I think implementing a similar system for the old BitMixer is a good idea. Some people simply wan't their cryptocurrencies to be untraceable via block explorers, and nothing else beyond that. Though I agree with you that it can cause confusion, especially to the newer or older cryptocurrency crowd.
This ofcourse can be implemented successfully though. Maybe add a small comparison section between ChipMixer and ChipMixerLite on the home page of chipmixer.com? Or maybe just add a slider on the top-right hand corner of the Step 1 deposit page, like YouTube's autoplay slider. Probably left for ChipMixer and right for ChipMixerLite?