A lot of Manjaro users I have talked to say that Manjaro is just Arch with an installer. However, this is fundamentally wrong!
Manjaro maintains a separate repository which is not in sync with Arch's main repositories which means Manjaro is not just Arch. To add to that, even Manjaro wiki states that it is not Arch [1]! To quote the wiki,
In fact, the differences between Manjaro and Arch are far greater than the differences between the popular Ubuntu distribution and its many derivatives, including Mint and Zorin.
Manjaro claims to be stable just by delaying packages for a week. This is not an approach a stable distribution would take at all!
If Manjaro had to be actually stable, it needs to hold back the AUR packages as well. It has to maintain its AUR that is in sync with the Manjaro repos.
Say that a package in the AUR depends on a library, say libxyz. And libxyz is in the main repos, not in the AUR. The package is updated so that it relies on the new features introduced in libxyz's version 1.1 however Manjaro delays packages so libxyz is still on 1.0 in Manjaro. If you update the package in Manjaro, it will break because Manjaro holds back packages. So the only way Manjaro can be stable is by literally forking all the Arch related repositories including the AUR and keeping them in sync.
Manjaro is not really a secure distro.
Their own updater had a security vulnerability which wasn't fixed until recently [2]. This is actually a core package, not an extra or community package. To quote the list,
I have discovered an issue with one of your core Manjaro packages,
manjaro-system
20180716-1 and earlier. The issue allows a local attacker to execute a Denial of Service, Arbitrary Code Execution, and Privilege Escalation attack.
The amount of attacks that can be done due to the vulnerability is a lot!
The Manjaro updater [3] does all the bad practices that one could do in
a general Linux system and Arch Linux system specifically. Each time
the system updates, they reinstall some packages to "fix" issues and
they use the --no-confirm
flag (force) everytime they do so and
various other odd sequence of commands which are just as bad, if not
more.
In an update, password less updates in pamac (Manjaro's AUR helper) were sneaked in and from the look in the issue [4] made concerning this, the change was made to look like a "feature". This is a major security issue considering that packages in AUR are not checked by Arch Linux maintainers (and Manjaro does not maintain its own either). Some AUR packages were found to be malware in the past. So think about a casual user (Manjaro's target demographic are not really power users) installing a harmless-looking AUR package that could potentially mess their system!
Manjaro let their SSL certificates expire not once but twice [5]! The first time, they asked the users to use a private window and/or change the system time [6]. The second time when the SSL certificates expired, they did the same [7].
[1] https://wiki.manjaro.org/index.php?title=Manjaro:_A_Different_Kind_of_Beast
[2] https://lists.manjaro.org/pipermail/manjaro-security/2018-August/000785.html
[3] https://gitlab.manjaro.org/packages/core/manjaro-system/blob/master/manjaro-update-system.sh#L34
[4] https://gitlab.manjaro.org/applications/pamac/issues/719
[5] https://www.reddit.com/r/linux/comments/4inrut/manjaros_ssl_certificate_expired_again/
[6] https://web.archive.org/web/20150409112614/https://manjaro.github.io/
[7] https://web.archive.org/web/20160512210401/https://manjaro.github.io/