Most new breed Docker hosts like http://tutum.co can give you a quick DIY version.
But in general they (Amazon) are (currently) the best of breed and I have only positive things to say having used the JS and Java versions.
Pros of IronWorker: More language support, better logging, easier to debug, scheduled tasks via API (this is the main thing stopping us going all in on Lambda).
Cons: Slower start up time (~2-3s on average compared to milliseconds with Lambda), pay upfront rather than pay for what you use, no choice re. CPU/RAM.
Edit: Oh, are you saying that you want to send an API call to schedule something? They say in the post that API support is coming, but I don't know if you could schedule a one-off run that way.
That said, a big differentiator is IronWorker's ability to be deployed to any cloud provider as well as private clouds / on-premises. Many of our enterprise customers need hybrid deployments.
We're always listening so please feel free to shoot us feedback at support[at]iron.io or find us at @getiron.
Chad @ Iron.io
The other big downside is every time your function goes "cold" you pay the cost of all the extra (anything not in standard lib, ImageMagick, or the AWS Nodejs SDK) libraries you need.
The upside is that you only pay for the time your code actually runs. I've replaced a cronjob server and saved ~90% on the bill to run my jobs. Mostly they were scheduled backups and other misc integrity checks on AWS and 3rd-party infra, so nothing that intense.
More limits/downsides: http://serverlesscode.com/post/aws-lambda-limitations/
1: the cost for 2 seconds of execution time on a 512-MB execution environment is 0.00001668 USD, so it's not likely to break the bank. If you have a high-traffic function it's likely to stay "warm" pretty much all the time. And if your function is low-traffic, it's likely you fit inside the free tier.