>>20064303PaD's pretty good, but if you aren't good enough to make minimum 4 matches per turn or are capable of saving 8+ heal gems without accidentally matching them you'd probably die in the event dungeons no matter how good your deck is.
The Rare egg machine is a worse crapshoot than Brave Frontier, but if you log in every day, sometimes you catch a 24-hour limited dungeon that offers a cash only unit as a guaranteed prize and is fairly easy.
and clearing those automatically gives you 1 gem as well.
I hoarded like 100+ gems over the past year. And then the Evangelion Collab happened. I used them all and have a full set, No regrets. the Shinji & Kaworu duo and Misato are ridiculous units to have. 
