We don't use SQL Sentry's Event Manager, but we use the Performance Advisor, and they are integrated together (need a proper license to activate one side or the other or both). Having used PA for a while, it's not flaky at all. We rather like it and it's helped us monitor and right-size servers, such as with a recent data warehousing effort we just put into production. We looked at Event Manager and liked what we saw, but we use an enterprise scheduler that also interfaces with the mainframe and it has its own built-in monitoring and reporting. So we didn't go ahead with the Event Manager license.
If you have questions about Event Manager, contact the SQL Sentry folks. They are extremely easy to get in contact with and they aren't pushy at all like some vendors. They used to be a huge hosted SQL shop, and Event Manager and Performance Advisor were developed to solve their own internal needs. So they're quite proud of the products, as you might expect, and typically go above and beyond to ensure you get a fair shake-out of it in your own environment.
K. Brian Kelley