No issue with doing it, I do it all the time. One piece of advice though. Always, always, always, do a test transaction first before working with any bank of any kind. I always initiate a $100 transfer, wait till it clears, make sure there's no issue and then, and only then, do I xfer the full amount and only do it FROM Marcus back to your origin account. This prevents any potential issue especially with incorrectly entered account numbers. It's no big deal to unravel a screwed-up $100 transfer, notsomuch a $40,000 one!

I've had the best luck with Marcus and Ally so you should have no issues. Quick transfers too.