Using a set of monitors that complete each other is a good idea I agree.
I have heard "Avantone MixCubes" is a good choice for secondary monitor.
They are not ment to blow you away but if it sound goods on them they will translate good on most systems.
Also In general doing reserach on which monitors that does translate best is also a good
idea. Genelecs for instance they do not translate well to other sound system, while it sound good
on them it might sound dull and boring on other speakers.
using analysing tools is good to see problematic frequencies that you might not here.
Yes the avantones seem a good choice for a ''second opinion'' regarding a mix..
I've read and discovered in person exactly the opposite regarding the Genelecs they translate superbly and sound good at the same time, especially the ones that use the ''SAM'' system that fix the room acoustics with a probe for calibration to the listeners position. Maybe your information is outdated? They are very, very serious about room acoustics and the way their systems integrate, a thing other companies don't care..And since I can't hire an expert in acoustic treatment to fix my rented house reflections, options are scarce don't you think?http://www.genelec.com/news/latest-news/131-news-archive/year-2012/928-genelec-introduces-new-smart-active-monitor-sam-concept/
I know gearslutz bash Genelec and maybe it's where you got that info, but I've listened to some recent models
and I was blown away...
For people with limitations regarding, little, or no room treatment, they look like the best option available, what is the purpose of buying a 4k monitors if your room is a shit and all you have is third party calibration options not tailored to your specific speakers?