i changed a lens on my I3 Pros for the 1st time 2 weeks ago, I had absolutley no idea what i was doing and had heard it was difficult to do, although it took me about 30 mins to do it, i didnt really find it that hard. If you have strong thumbs you will be fine.
I like the I3's better then the Vents, but the vents are much easier to dismantle reassemble especially if you have a fast turn around between games...
At the end of the day, its all down to personal prefference