I will write this review according to my personal experience and according to my limited technical knowledge, because I am not a "computer security expert", a blockchain developer, nor am I a kind of user that requires absolute anonymity in the blockchain. But I do have questions and personal opinions, and I might have found some things which could help Tumbler.IO improve their service.

Mixer Name: TUMBLER.IO
Test Date: September 30, 2024
Reviewer: Wind_FURY

Introduction

- Tumbler.IO is a Bitcoin MIxer that obfuscates a user's transaction trail, and like other mixers/tumblers, it also helps increase the network's "anonymity set".

Impression

- The website's UI/ UX is very straight-forward, very easy to understand, and everything a user needs is easy to find. Because it uses a modern framework based on Javascript, it's also very functional in small screens/mobile.

The Test

- For my tests, I did it in two parts. The standard, "I will use the default settings" test, AND the premium "I want to be more anonymous" test.

A. Default Settings Test

- This test was done in a mobile phone, with a Safari browser. Everything was very easy, simple, and designed that newbies who had basic knowledge can use the service.



- There's actually nothing more to say except for a "critical privacy" issue warning from BlockChair, which might not be an actual issue for this test, but I possibly found an issue in my premium test.

B. Premium Test

- In this test I used a TOR Browser, I used a higher fee, and added one more receiving address. The website worked perfectly. No issues with UI/ UX, BUT I need to say that I used the TOR browser in default settings, without script blocking extensions.



- But I may have found an issue. I checked the transactions of the change address of one of the senders, and I saw another transaction that might be by another fellow tester? I checked both of my receiving address and I can confirm that it isn't mine. If it's actually an address by a fellow tester, it could be a serious issue for everyone who uses the mixer.



Other Comments

- It's mentioned in Tumbler.IO's Terms that the mixer might use a service of a third party to filter outputs. My          fellow posters in the forum know that I believe there's nothing wrong with taking this trade-off to protect itself and its ability to provide a service. BUT it opens a can of worms because how can the users refute a false positive?
         
The filtering entity could always say that a positive whether true or false is proof that the system works, but a "false negative" is merely because it's not filtering restrictive enough.

Then instead of helping increase Bitcoin's anonymity set, Tumbler.IO might be its own problem to the vision it has set for itself.

- Accept Lightning transactions. I'm not sure about the implementation, but It's probably good to give the users a choice whether to send their coins on-chain or off-chain through Lightning, not because it's cheaper, but because it adds another layer of anonymity and privacy.

- Fees. They're high. Although because of my own understanding and belief of what the Bitcoin network should actually be, some of the time I don't mind paying for higher fees than average, but like my fellow testers' suggestions, if you could make it lower, then make it lower.