Do not switch away from your theme if you like it. You'd lose it for good.
If you currently use Flexible Squares s2flexisquares or another older s2 theme as the base under your layout and like it/like the features it offers, do not switch to a different theme ever! Old s2 styles were dicontinued and you can't choose them anymore. If you even so much as try a different theme on you won't be able to get your old one back (unless you have a paid account and re-create it manually.