The JJ and Inspiration were designed by the same person. The JJ improves a whole set of physical things that are not ‘features’ you’d see in a brochure. If is made out of metal, the Inspiration has a 1960s sci-fi case made of plastic, it doesn’t have an o-ring loose and forgettable when you replace the sorb, the JJ plastic parts are machined not moulded.
The philosophy is different too, many manufacturers add stuff to cover potential issues, the JJ is quite simple. Does the temp stick really help? Does a CO2 monitor? I looked at both and I would definitely have ordered all the options on an Inspiration - I have a BOV on my JJ - but the case and, at the time, nasty handset put me off. I do know lots of people with Inspirations though and they are all managing fine.