When to make the switch to featured crystals....
As a side note, if anyone has spreadsheets already made for either of the featured crystals, they would be very welcome.
On to the main point. How deep of a 5 or 6* roster do you think is necessary before a summoner should start to consider the featured crystals seriously? This is not taking into account just really loving a specific champ, or the odd fling, but when would it make sense for them to seriously consider opening one or several featured crystals?
I know the math basically always favors opening the basics because then you will accumulate more champs and higher shards/etc. over time, but that is what makes this a subjective question.