Invertek is one of the few single phase drives available. Plenty of people make drives that accept single phase and put out 3 phase, but there are only 3 mfrs of VFDs that I know of for single phase MOTORS. One reason is, there is only a narrow range of TYPES of single phase motors that they will work on without damaging the motor and/or drive. They cannot be used on any type of capacitor start single phase motors, which only leaves Shaded Pole and PSC (Permanent Split Capacitor, because the cap is always in the circuit anyway). Shaded Pole motors can also be controlled with simple cheap voltage control, so it really leaves only PSC applications that can use them, and that is a relatively small market. That means the volume is low, so the price is higher than an equivalent 3 phase output version, which leads many of the remaining customers to just replace the single phase motors with 3 phase and get a more readily available drive.
All that said, there is nothing wrong with the Invertek drive, they make a decent product. You can buy that drive brand-labeled here in the U.S. From two companies; Bardac and Anacon. Google will find them both for you. The other two versions are small niche mfrs who cater to the HVAC business where people must put a VFD on bathroom **** fans so as to make sure they don't upset the air pressure balancing. Those other suppliers are not what I would consider an industrial grade product, yet tend to be more expensive than Bardac and Anacon.
If your blowers are not using PSC motors, you cannot use a VFD. You are better off replacing the motors with 3 phase, then get a good off the shelf VFD from one of the major players that will take in 230V single phase and put out 230V 3 phase.
