As mentioned previously I'm leaving a quick review for the site as I've recently used it.
I've used a few different mixers, this site locks down a few options to improve security and avoid common mistakes like setting an immediate return on the mixed funds. Having the site determine factors raises variability across the population of users on the site and helps diversify away from common preferences that may lower security and quality of mixing.
Having such a straightforward interface makes it incredibly straight forward and fast to use, its literally one page, no sign up, no emails, no login, no passwords just save the letter of guarantee when given for the duration.
I saved this briefly and just sent it to myself encrypted via a 2FA email account of my choice but people can do whatever they want which avoids any common point of attack or vulnerability in the whole process.
Like Loyce I used a lower fee to transmit funds and it did not clear the next block, its not required and the site will acknowledge the transmission and then wait for the normal confirmation times however long that fee may take, I believe the process is left open for 7 days to accommodate peoples personal setup and any delay in the blockchain so there is no worry or rush.
The only brief hitch I had was to use a Coinomi wallet which defaults to a native SegWit address bc1 type. This was the 2nd address required for the spare change part of the mix, I switched it over to compatibility format which makes no difference to me and that address I entered was no longer highlighted in red and I was able to receive the small amount of change fine.
The main address I used for receiving my mixed funds was just a normal website address and as normal they give out the most compatible type and that worked fine. Despite me using a low fee initially which delayed confirmation for a few blocks, the process of mixing was faster then I thought as it said upto 6 hours but most of the time I believe it would be closer to an average under half that time. By not giving a fixed time, the security is raised and I believe that decision is correct for the best care of all users in the primary use of the site to retain anonymity.
At the bottom of the front page is a calculator to give a rough idea of the fixed and % costs to transmitting whatever amounts you had in mind. Almost all the funds will go to the primary BTC address you specify as indicated by the calculator, two addresses are required as I believe it improves security and anonymity. I can recommend the site to the general public for being so simple to use and 'doing what it says on the tin'
[Just to update, I did receive the reward and coverage of costs mentioned in the OP]
So I tried precise payment option yesterday. In short, it is a nice and much-needed feature especially if someone is mixing funds to further use them to make specific payment from the destination address. A nice option to avoid leftover on the destination address. 