They often include mechanics that would be impractical in regular Magic, such as summoning random creatures from your deck, creating new cards, or permanently altering others
I have no idea how much more often the uncommons actually show up compared to the mythics, but anecdotal evidence (talking to lots of people who have opened lots of Collector Booster boxes) seems to indicate that each box tends to have at least one or two Showcase Gods
but at the same time, if your synergy is sound, you can put together some solid decks within the limitations, and then reap the rewards of these powerful new Glimmers
They can be played alongside high-cost cards in order to spend your extra ink and develop your board, they can get buffed by a Support character like Rolly and become a cheap way to trade up into bigger threats, and Lucky can discover them when you use his ability Good as New, making them more valuable in your deck than in your hand
Depending on how many you have in your deck, you can hit for at least 4000 points per turn
While losing ink from your inkwell may seem like a deficit, the cards are returned to your hand, giving you back some of the options you may have sacrificed in the early game to gain ink