I repair electrical controls for a living.
As much as I hate too admit it, the more complex something is the greater chance of it breaking.
If one half of the combo unit fails, you have to replace the whole thing.
A stand alone inverter can be picked up at many auto parts stores, harbor freight, probably at Sears and Wally World.
A converter isn't much more than a transformer, 4 diodes, and a regulator chip with a control transistor. If/when the diodes go bad, New ones can be installed very cheaply.