This is an update on the Endura MT500 Waterproof shorts.
So far the shorts are holding up very well, just washed them the other day and they look brand new. They breath extremely well, I sweat when it's 0°C out and I haven't had a soggy sweaty diaper afterwards. As for waterproofness, I haven't had them in a heavy downpour yet but they've been covered in mud and water and they've kept me dry. I hosed the mud off them when I got home with a fair bit of pressure and the water just bounced off the material, no water penetration whatsoever.
Very happy with the purchase!