There are concerns with these exchanges, but they are fiat related rather than crypto. However, I would always advise to keep your funds of exchange unless you want to trade in the near term.
That is an advise we have to always follow because these exchanges are also having some problems of their own and if we get so unlucky our funds (or coins) can get stuck in them and may even go down with the ship should there would be a collapse.
It happened in the past and there is no guarantee that it would never happen again. Exchanges can go down into the tube if not done properly and if market conditions beyond their control can occur.
It's very strange why else Bitfinex, I flew into the pipe after last year's hacking incident with hackers of their servers. Perhaps they still have gunpowder in the flasks.