Same here. I'm asking what the reasoning of those willing to switch to One is.
If they didn't get the November promo, it can make sense to take advantage of kickback for lines using less than 2gb of data and also if they need the extra 3gb of LTE for the hotspot. Also they can sign up for t-mobile one plus for $5/month/line gogo unlimited (not worth it) and 2x data speeds abroad (256 kbps won't get you anywhere, so I just get a local SIM that I stick in my iPad). I think in the long run T-mobile will introduce more and more promo limited to T-mobile ONE accounts, but I will just wait until they decide to discontinue it and offer to match all my free lines.