I love the fact you talked about the swiftness of the support team. Many establishment takes this lightly but this is a very serious aspect of their relationship with the customers
Using financial sensitive platforms like Bitcoin mixers requires lots of security consciousness. And I won't personally trust a random person compared to the support team. So if the support team works fine then it's a big plus to the project.
The relationship between the customers and an established enterprise need to be strong to ensure there is a mutual bond that will keep users to continue using such service to get their problem solved without any negative experience. Since we have so many mixers online that users can set their hands on to mix coins, it is advisable for a good mixer to create a continuous bond with users to keep the inflow much constant.
New users especially the ones that are new to mixing might find the process uneasy making some complicated mistakes that could lead to lose of fund or difficulty in output. This would never be a difficulty task to be resolved by good and reliable mixer which is the reason why one need to use a good mixer for conjoining of coins.
If we are to be talking about easy to use mixers, then I can you tell that Unijoin is definitely one of the those, in fact, one of the best in this regard, the step by step procedure to mixing coins ensures a very easy to understand process, guarantees zero mistakes what so ever, except the user wasn't paying enough attention and mistakenly submitted a wrong address in the process, that can I believe can still be fixed if the users notice it on time when mixed coins havent been sent to the wrong address, but let's say this somehow results in the lose of fund, this absolutely Is no fault of the mixer as we all can agree.
So, in all, I agree wit all that you said, the coinjoin service is one that is beginning to look like online gambling casinos with new mixers launching almost every day, But then, the best mixers will always survive no matter how high the competition gets.