It took a slot of Feral Bonds in my anti-FG rainbow now, going on 3 days. Had Bonds + 3 shards, where Bonds will provide massive healing against poison and assist greately in EMing. Now Purify can do pretty much all of that, except it also lets me stay alive early game (when I aint got no creatures out yet, or aint got a quint) and does freaking miracles against poison gods (e.g. scorpio and morte). Definitely a good change, the card is perfectly playable now.
In abstract, Shards are better. However, there are many FGs with no-joke perm control capability where I'm pretty much always happy to draw this. As an added bonus, it is not liable to "steal" some critical quanta in a tense moment, and like most others, my rainbow only uses
for Permafros so there are always spares around