There is something a bit 'hmmmm' about them. I have just bought my third, an Airsporter-S, and it seems quite nice. It is very well made and has a lovely walnut stock and proper metal open sights. It's got a special Zephyr piston head on it too, just need to go and test it on the range with different pellets.
I had a rough Airsporter Mk 2, overhauled it and couldn't get on with the trigger. Then I had a pristine RB2 Stutzen, which had a decent trigger but I just didn't like the feel of it on discharge, felt like it was really an FAC gun and with the standard spring it felt very 'boingy and soggy'. Sold them both.
I remember asking Dave Welham of Airmasters about the Airsporter once and he just said 'horrible guns, can't do a thing with them', while John Bowkett seemed to make some which shot very well and with little recoil.
Another 'Marmite' gun perhaps?