I use Shutterstock on occasion, but only buy credits vs. a subscription. I avoid subscriptions as often as I can because they appeal to your sense of a good deal/bargain, but rarely pan out to the extent you originally envisioned.
My issue with Shutterstock is that they default to auto-renew credits rather than default to not auto-renew. The vast majority of clients will purchase credits based on their current needs. If customers wanted more, they will buy more, and do not need Shutterstock to "conveniently" automatically buy more credits. It's like having a drink at the bar and the bartender automatically filling your glass when you finished because you have a tab open. Yeah, it's nice to have that option, but, no I want you to always ask before spending my money.
Seeing all the overwhelmingly bad reviews really confirms how little Shutterstock values customer experience.