You probably mean a previous installer to Calamares. Calamares is used by many Linux distros.
Not sure, I think Calamares was introduced with OMLx 3.0. I am pretty positive the ROSA installer for Mandriva 2011 and OpenMandriva 2013 & 2014 did not have this feature.
You are talking about checking the checksums for an .iso file. This is easy to do and does not take long. Like a few minutes or less.
Checking checksums to verify integrety of OMLx .iso files
One should always check the checksums for an .iso. However the fact that the checksums match does not guarantee that there will be no problem, it does make it less likely.
Another thing I do with .iso files is I do not download them with a browser downloader. I always download them in Konsole (terminal) with aria2c or wget, curl is OK too.