Flexibile but not without frustration
For me, the flexibility is a huge plus! Once you get past the initial learning curve, you can quickly whip up an IQA to report on just about anything. The modularity of the iParts makes it relatively simple to build a functional website together quickly, and with a little more time and effort, you can make something truly impressive.
As for downsides, there is a steep learning curve that non-technical users may find daunting. Especially so if you have been dubbed the unofficial iMIS Administrator for your organization (a predicament surprisingly more common than you might imagine!) I found the lack of documentation for some features to be frustrating, and you will have to look to support partners and outside resources for answers. When getting started, expect to sink a considerable amount of trial-and-error time to get your IQA queries and dashboards working satisfactorily.
All that said, for a small organization with limited staff, we have found iMIS to be a real timesaver. I would add that my experience with ASI support has been super-positive: they have always been helpful and responsive!
