Definitely wasn't make or break, but I've certainly been transitioning most of my assets out of Polo because of this and some other oddness I've seen there for the last month+.
They can't be beat for liquidity, but I can't imagine they're not complicit to some extent in market manipulation.
May I ask what exchange you are transitioning to?
I have used Poloniex for the past couple of months. Only had a few issues until this week where it now seems like the lagging is affecting trade in many altcoins. Have a little on Bittrex which seems to be working good. I don't want to get into exchange hopping but I probably should spread across more exchanges.
Yeah I've never had any major issues with polo other than the odd few minutes of lag. I mean even now its not that bad but I guess when you are margin trading it can make or break you.
As for the class action suit ultimately it will fail, its part of their terms that they can't be held responsible for lag and its not like they physically stole any money from anyone. So unless the allegations of insider trading can be proven no one will get anything back.