The 750XL does have the uncomfortable 'Gippsland Aeronautics' crew seats but I found that a thin cushion behind the lower back works wonders.
Remember that it is still early days for this aircraft to be 'known' as a utility aircraft as opposed to just a skydive/top dressing machine but don't write it off. They are a seriously capable bush machine and the factory has been proactive about listening to their customers and working on shortcomings.
Their numbers are growing in the bush and for good reason. You can take them places you wouldn't dream of taking a Caravan let alone pull a decent load out of the same place!
Check out the videos of it on YouTube operating in PNG and Africa and the factory promo
Pacific Aerospace: P-750 XSTOL Video
Far from being breakable plastic, the thing is tough as nails and I would take a 750XL over a lot of other aircraft for rough bush work. In the hands of an appropriately skilled pilot they can really haul.