Rytr.me was my desperate 2am solution last month when facing a deadline for my comparative lit paper. My honest review after trying it on several essays:
PROS:
Does a decent job with simple, straightforward content
Interface is pretty intuitive
Quick results when you're in a time crunch
CONS:
Absolutely butchers complex theoretical concepts
Has this weird tendency to make everything sound like a marketing brochure
Sometimes creates sentences that are technically correct but sound completely unnatural to human ears