Jar is okay, but it's a one-shot card boost and does nothing the turn you play it. I think for 1 more mana The Immortal Sun is better. It stops PWs and shops run none of their own, beefs up your weenie plan and shops is mainly aggro now, gives you incremental card advantage spread out over turns so you can cast all of it instead of the best 2-3 pieces out of 7 like jar, and negates one of your sphere effects on yourself. If you want a CA engine with plus side, I think TIS is the way to go nowadays.
I ran it today in my sideboard for an invitational where I was expecting to see a lot of shops matches. I had it once and it did exactly what I expected - drew it mid game, played it while I was slightly behind on the board and just flipped the board state completely. Unfortunately I missed 2 sacs to a ravager later that cost me the game. But if not for memory jar, I would have lost probably 2 turns later. Instead we went another good 8-9 turns.
I rather enjoyed having it in my side for the mirror. I dont believe I would want it against any other match up. This is also the first time in 2 years I've run shops so I'm hardly an experienced pilot.