I think you can do the math yourself - the costs are published.

FYI - we did some experiments and the limiting factor was latency. 250-300ms on average, you have to go through their API feature as well, and that's part of the delay. But worse - Lamda's that have not been called for several minutes (I'm assuming they are not 'hot') often take several seconds, up to 5s to be called. So it creates a problem for intermittent traffic.

If that kind of latency is acceptable to you, it might work for you so long as the cost equation is right.

I think some other people had issues with versioning, it's a problem we didn't go far enough to observe.

I'm not using it for anything like this, but I am using it for production. I scrape CloudWatch metrics into our standard time series metrics repo. Total cost for every service I care about (ELB, ASG, RDS, ElasticSearch, SNS, and SQS) has been about a dollar for the last 3 months.