Can't say I'm exactly over the moon about this. Although Atlas does seem to be quite a bit cheaper and probably offers a better implementation of the product, mLab's key offering was always the incredibly good support they provide as standard. I haven't needed it often, but I know I can rely on it.
Atlas does not include this - it's something you pay (a lot) extra for and I'm pretty apprehensive about whether it's actually going to be great support or not. At this point my primary worry is that it's going to be more AWS-style support, i.e. expensive and total crap.
The fact that there's no mention of support in the email or blog post does not fill me with hope.
Any Atlas customers who can chime in with their anecdata?