My biggest concern after reading about Fastracs was the reliability. Got a 5 year warranty on ours given these concerns. Problem is if it goes down at a critical time we don't have another tractor that could pull the sprayer instead just like that, although given ISOBUS it could be done with some new hydraulic fittings. Have 1000 hr service coming up and a slight grumble in the diff with 4WD which I need to check (might be something I'm doing).
Never driven Fendt, so can't comment on their comfort, but can certainly say that the 4220 is just in another league compared to the Masseys we had. If you're thinking about a Horsch, one of the key strengths is stability at speed, and you need a comfortable tractor to make that doable from an operator's point of view. I had a sore back before and now it's gone despite having spent 750 hours in it this year. I almost wouldn't drive anything else now. 4WS does mean a bit of extra complexity and button pressing to swap between the two modes (Topcon doesn't steer in 4WS very well so use this at either end of the field). However, I find backing the sprayer into corners a LOT easier with 4WS as you can pretty much put the boom where you want it (almost easier than a SP now I've got used to it).
Only thing to think about with the trailed sprayers (especially a GS with a long wheel base) on 36m is that it's so long that you don't have much room to switch boom off and turn except in perfectly square headlands (this is again exacerbated with Topcon because at the moment I'm struggling to get it to model a steered trailed implement, but have been told of a trick to improve this which I need to try).
can you get the sprayer to steer in the 4ws tractor wheeling on turns leaving just one track or is that not possible ?