It's more than an installer. Manjaro and Arch don't even share repositories.
Manjaro Live OS can't be used to install vanilla Arch. Manjaro uses its own package repositories that differ significantly from the Arch repos, in terms of versions (which are held back for at least a couple of weeks) and in terms of which packages are available (quite a few AUR packages are present in the Manjaro's repositories).
Only recommend using them for subsequent installations. You have to get the basics right first, so you can troubleshoot anything in the arch forums
It is very, very promising. It spits a JSON that can be used for reproducible installs. It is also very flexible in which you can use the API with custom python install scripts. Very impressive and ergonomic.