It should be easy to reach the service provided that Google doesn't list fake lookalike websites[1][2][3][4][5][6] instead of the original - real - one. Due to issues such as the one mention before and a massive DDoS attack, ChipMixer decided[7] that the clearnet address would only be informative. Like others said before me, there's currently only one way to access ChipMixer:
LoyceV also left this information on the official Chipmixer user account[8] to make things even more transparent. I understand that, at first sight, this decision may look like that Chipmixer is "hardening" the access to their service but in reality they are just trying their best to protect their customers (and service).

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[1]https://bitcointalk.org/index.php?topic=5318195.0
[2]https://bitcointalk.org/index.php?topic=5318195.msg56388168#msg56388168
[3]https://bitcointalk.org/index.php?topic=5406044.msg60557690#msg60557690
[4]https://bitcointalk.org/index.php?topic=5406044.msg60557690#msg60557690
[5]https://bitcointalk.org/index.php?topic=5272178.msg55094411#msg55094411
[6]https://bitcointalk.org/index.php?topic=1935098.msg60403691#msg60403691
[7]https://bitcointalk.org/index.php?topic=1935098.msg60186638#msg60186638
[8]https://bitcointalk.org/index.php?action=trust;u=1003345 - clearnet address just informative as of now.