Hi ucity!
You do not need Ermine. It is a system upgrade that takes the Android in your eDGe to version 2.2. You probably have Android 1.6 right now. Ermine also makes some other changes, the biggest for me being it allows the eDGe to hibernate when closed which saves battery usage.
Do you have the big enTourage eDGe or the Pocket eDGe? They both have problems (for some of the people some of the time) with Ermine, but the problems are different. It is possible to get the "White Screen of Death (WSoD)" when you upgrade to Ermine on the PE. If that happens (fortunately, it is rare) your LCD will turn white and stop responding. So upgrading is a risk, but if you succeed there are rewards.
Ermine is a "beta" update, meaning it was never finalized by enTourage or guaranteed to be bug free.
Happy decision making!