I've used the Ultrastem and Ultrabar in 25.4 on my cargo bike for a few months with no issues. All I had to do was add a drop of loctite to the faceplate bolts.
I've also been using their Ultralever 2 brake levers for years on my MTB and put another set on my cargo bike from new. They're my favourite cable MTB levers by far.
I also only weigh 11 stone though. :)
I have also used Smud saddles and seatposts for years on MTB's and my work bikes with no issues. For me the quality of both companies has given me no concerns...whereas I've broken thomson stems and seatposts over the years. I guess it's just bad luck sometimes.
Edit...I should add, I only stopped using the Extralite stem and bars on my cargo because my custom loop bars eventually arrived, and I also needed a slightly longer stem, and managed to get a cheap Thomson in the right size.