[Discussion] How good are limited UR skills

Most people who occupy the top score rankings use the lim AC Umi. This makes me wonder, how good exactly are the lim UR skills. Do you think those limited UR skills are better than the normal UR skills? Which lim UR skills do you think is good/bad? Are spending gems on lim boxes to get cards with these skills worth doing, competitively speaking? Also are they better than the birthday cards score up skills? What do you guys think