Is Magic Trackpad feature-equivalent with built-in MacBook touchpads/trackpads?
Yes, the Magic Trackpad or Magic Trackpad 2 should allow you to test gestures and work out if they're user friendly.

The only problem I can see is if you have very odd gestures or use of the track pad that relies on the specific physical size of the trackpad (which is normally not the case). The size of the trackpad varies from Mac to Mac (i.e. older models typically have smaller trackpads).