Thermafusers work well as long as your supply static pressure is .25" or less. Anything above that and they won't close down sufficiently. We've had good luck with the LON based units and when coupled with a VFD - you can do a pretty good job of zone control and no wall mounted thermostats to deal with! Plus, with the networked LON Tfusers, you can monitor CFM , supply air temp, and terminal load as well as adjust setpoints. On DX systems we use supply air low limit strategies to prevent coil ice-ups. Placement of the diffusers in the room is also important in order to ensure that the space sensor located in the face of the diffuser gets proper air induction and reads an accurate space temp.
I also like the auto changeover feature that detects supply air temperature and switches heat/cool modes.
Their support has always been good too.
A hundred million nodes - it's a LON story.