I was offered a ride in a G140 (the only one then flying, and I don't think they have more than one even now) in 2004. I just had to get myself to some German airport.
But I didn't have the money to buy it, not by a long way, so didn't see any point in wasting their time.
It would have been quite an experience though... 450HP with (probably) 1400kg.
As a VFR+IFR pilot I would have bought the G140 on the spec sheet alone, if I had the money. It's got the exact perfect European touring + messing-about mission capability. And I am not in the least interested in aerobatics.
As to demand, as I said they need to get the price down a bit. They have done the standard aircraft marketing trick of developing an expensive plane (nothing with a turbine will be cheap) so they load it with nice expensive avionics to make it look worth the money. It's undoubtedly a very good package but I am sure that if they were doing it today they would just screw in a G1000 glass cockpit; not because it's good or of proven reliability but because everybody else is doing it so "it must be OK". The price would come down at least £100k with a G1000.
Unfortunately, Grob seem as intoxicated as everybody else with the light jets. There will be a bloodbath in that market; I guarantee it.