I owned a 2006 spacecab XF 480 AS TRONIC from brand new until last year.
Yes it is a little difficult to master shunting forward and reverse but when you do it is no problem at all.
Yes it is a little slower to change from neutral to either forward or reverse but easy to get used to.
I see driver after driver moaning and complaining about this gearbox but I honestly loved it! I found that if you drove it like a constant mesh gearbox when slowing down or coming into a roundabout (brake,blip the throttle,it drops a gear,pull away from the roundabout),drivers forget that although it’s automatic it can’t read the road ahead and needs to be prompted,sometimes on sharp hills and narrow roads it is best to just drive it in manual. Yes the Volvo Ishift is much smoother and far easier to manouver but I think it’s far less fun 
With that truck I did multidrop pallet work (up to drops 30 a day),continental work to Germany,Austria etc pulling euroliners,and the last 5 years hauling re-bar to building sites with most of them being windfarms up some very steep mucky hills. I have to say that the gearbox didn’t give me one bit of trouble,never laid a spanner on it or the clutch,sometimes when shunting it would get confused if rushed and not select any gear,simply turn off the engine,take the key out of the ignition and let it settle for about a minute and all would be good again.
I think I know the truck you are looking at and was considering taking a look at it myself but the crane was a bit small.
Dafs are good trucks and the 480 matches really well with the ASTronic gearbox,keep it serviced and it should be a safe bet.