I usually use Notepad++ to do most of the work when creating rulesets. But when testing out new ideas or making minor adjustments, it's nice to be able to do it in the GUI. However, the method of choosing numbers or techniques is very frustrating. Choosing from a scrolling list of 128 numbers, starting from zero every time, is particularly painful.
This is mostly because of the way the scrolling system is implemented, where you have to click and hold an up or down arrow to scroll, or use keyboard arrows. For techniques, you can enter the first letter of the word to get closer so it's not quite as bad.
The GUI would be much more usable if scrolling were better implemented, using typical modern scrolling techniques such as a scroll bar, hovering at the edges, and rolling the mousewheel. We should also be able to type multiple letters/numbers to get where we want to go. Typing "83" shouldn't jump back to "3". The way Windows Explorer handles this when browsing files is the best example, typing in quick succession is assumed to be one word, pause long enough and it assumes you're starting over. And when there's already a number entered, the dropdown list should start from the existing value, not back at the beginning.
Alternatively, it would be helpful if we could type in numbers directly, at least.