Cartomancy in concept could be really cool and fun but its execution leaves it looking a bit lack luster, the issue is that the recipe for the conjuration crystals is too much effort for an ability that has so much potential to give you a useless buff for the content you're running at the time.
Don't get me wrong the buffs carto gives are super nice but nobody needs "increased commerce movement speed" or "increased gathering speed" during crom or glenn HM which apparently are more likely to happen than you'd think.
The way the buffs are balanced is nice but the fact that its random and once you cast it you can't reroll it at all for 36min makes the skill a bother to use and honestly I find it a bit silly that a skill of a class who's theme is tampering with fate gives you no way to bend fate to your will.
But aside from that one very real issue is rigel crystals, in order to buff your entire party you need 8 conjuration crystals, to craft 8 of those you need 8 rigel crystals (which is 120 rigel fragments, 16 flint and 8 bottled water), 16 unknown ore and 16 long nails, a lot of these mats are easy to get with the exception of rigel mats, I'm not sure if its just me but they seem to be the least common of all the constellation casting mats getting about 2-4 catches per in game night cycle so lets set the average to a 21, with an average of 21 fragments per night and we cant fish during the day so thats 21 frags per 36min, to get 120 you need to fish for about 6 nights which is 3hrs 36min, in order to get enough for one cast without getting lucky and fishing crystals straight up it easily takes about 3hrs 36min for a buff that more often than not will give you an effect that will hardly benefit you in your current task, the way the skill works you're not meant to use the skill when you need it but rather use the skill and do a task based on the buff you receive, and that's just not efficient at all.