Hi there. I have both! XD
I DO think it is helpful. Generally the stock is of much better quality, and there's alot more of it.
As far as plans go, Adobe now offers the same plan sizes as Shutterstock. The only difference being that Adobe i believe still only has an annual plan where you can do month to month with Shutterstock.
Both allow you access to your licensed material even after your subscription ends.
And both have most of the same stock. I believe shutterstock has a bit more options stock wise but tic for tac, theyre pretty identical.
OH! And you can almost always find a 15-20% coupon code for shutterstock. :D