The downsides are:
1. You have to put the iPad into supervised mode, which requires a full factory reset through the Configurator. This is because it enables a bunch of enterprise controls that they don't want enabled without the user's knowledge, such as the ability to configure a global HTTP proxy, etc.
2. As I mentioned before, there is literally no way out of the app other than removing the configuration profile. This sounds like it interferes with your use case, but maybe it's a worthwhile tradeoff for you?
3. Probably something else I didn't think of.
Here are a couple articles I found that mention how to do this:
[0] and [1] are articles from some app that this feature is useful for, explaining how to do it for that app.
[0]: http://support.kioskproapp.com/knowledgebase/articles/413366...
[1]: http://support.kioskproapp.com/knowledgebase/articles/315259
Disclaimer: I have never tried this myself, I have simply happened to have heard of it. I found the two articles above because I knew the term to Google (not a shot at you, sometimes you just need to know the right search). There may be some unintended consequences because it's an enterprise feature and all.
I find it quite a usability improvement, when using the tablet as a cookbook for example.
I really want to do something like this when I get my old house back this summer. Thanks for the inspiration!
[1] - http://www.openhab.org/
I've fantasied a dashboard of tasks and chores I need to do when I get home from work.