Aside from the point of keeping full control of your money and not leaving it in the hands of others, I've had very good experience with mcxNOW.  The only reason I could see to "worry" about leaving money there would be the usual issues one might have with /ever/ having any of your money out of your own hands. 

That said, the exchange is very stable and very fast.  By far the best out there, to me.  New features are added after much obvious testing and security appears excellent. It's run by an expert in both cryptos and in websites, but more than that, it's a professional application behind the scenes.  Real good stuff.

Regarding the ads, I was a little annoyed by the thought at first, but then it took the form of something more like a community bulletin board of sorts.  It's actually interesting to read through, as it gives a glimpse (for now) into the community that trades there and into who is vying for the eyes of folks interested in crypto.  I sort of dig the ads -- which is strange.

BTW, it's a simple fix if you don't want to see them: just resize your browser width a tad and poof! They're invisible now!  (Yeah, yeah.. adblock. Whatever.  I never run anything full-screen, so I'm not bothered by leaving the ads running and occasionally full-screening to see what's new.)

Blabber much?  Yes, but the more I have issues with other exchanges, the more I realize just how great mcxnow is.  Fanboi or not.