I took the nano SIM from my Verizon iPhone 5 (unlimited data) and put it into my iPad Air with it powered down. Once it came up, not only did I have LTE data but also personal hotspot since it was enabled when I set up the T-Mobile account. It works awesome. Another option if you want the best of both worlds.
How-to
1-setup T-Mobile account on iPad (free 200mb option)
2-Restart iPad to get personal hotspot if you don't see it after setup
3-Power down iPad and iPhone
4-swap SIM's
5-power up and verify connectivity by turning off wifi, you should still have personal hotspot available
6-after swapping SIM's back you see the NO SIM card warning, simply take out and re-insert the SIM into the iPad.
I did NOT have to alter any settings to get it to work.
How-to
1-setup T-Mobile account on iPad (free 200mb option)
2-Restart iPad to get personal hotspot if you don't see it after setup
3-Power down iPad and iPhone
4-swap SIM's
5-power up and verify connectivity by turning off wifi, you should still have personal hotspot available
6-after swapping SIM's back you see the NO SIM card warning, simply take out and re-insert the SIM into the iPad.
I did NOT have to alter any settings to get it to work.