I have had mixed results with sensor and sensorless VFD's, The ones I found good were Schneider Altivar series and Mitsubishi.
I have a couple of older style Mitsubishi VFD's on a couple of mills with original Pancake style induction motors, the flux vector sensorless will show excellent torque down to low rpm, and will accelerate faster than on straight 60hz and will stop on a dime without faulting, the encoder feedback version would O.V. on decel, so I had to put an external braking unit, now they match. They both use 120hz tops.
I believe the later ones do not need the external braking.
This is a site showing a few manuf. opinions on sensorless.
http://www.manufacturing.net/ctl/article/CA182473.html
Al.