My experience is that vertical keyboards only alleviate some problems and even cause new ones. They do relieve pressure from the ulna and radius being in a twisted position and they obviously relieve pressure from the side of the hands. On the downside, they put strain on the shoulders and neck since the arm is held freely in the air for prolonged time. Vertical keyboards also don't help with issues due to spreading ones pinkies too far for reaching control, shift and enter. For me the Kinesis Advantage was overall a far better relief. None of the measures I tried were however more effective than stretching and upper body strength training.
I had the problem despite of arm rests. Keeping the hands in a lifted position was the problem, moreover even a slightly bad pose caused my hands to bend downwards to reach the keys, which is also suboptimal. Armrests themselves are not optimal for supporting the arm because the surface area is small and hence the pressure is high.
