The i-magic is super as well. No 26mph issues (does not look like they will ever fix that) so you can do intervals, etc. up and down hills with no issues.
I find that the power measurement is occasionally right, but often not very close to my PTap when not climbing. I could definitely futz around with calibration some more to get things more accurate.
I am not sure why anyone would get the Fortius over the i-magic - the motorbrake of the Fortius allows you to coast down hills w/o pedaling. This will allow you to ride "junk" miles inside, I just don't see the point of that.