I just started trying out Affinity Designer Beta and I was trying to "ink" some pencil art I scanned in. I'm using the "brush" tool with the variance set at 100% trying to get good varied line widths. I trace the line and the preview, as I'm drawing the line, looks correct but when I lift my stylus, it's nothing like the preview. It's either all thick or it snaps back to being a thin wispy line. Even changing my sensitivity in the Wacom "Tip Feel" preferences doesn't seem to help much. Am I missing something? I'm using a Cintiq Companion Hybrid and also trying it with a Wacom Intuos Pro. Same thing happens on both. Trying to work on the same file in both Adobe Illustrator and Affinity Design to compare the feeling of the different programs. The Adobe "brush" maintains the preview format pretty well while the Affinity "brush" seems very random in when it will and won't retain the preview properties.
Macbook Pro 15" (late 2011) with 16GB RAM running Yosemite (completely updated) - Tablets tried on : Wacom Cintiq Companion Hybrid and Wacom Intuos Pro Medium with latest Wacom Drivers.