I've been using it for Python mainly but I find it's really helpful. It can often infer arguments for functions or functions to use based on the variable names. I've used Ruby lots in the past and I think it would work just as well based on my experience. I would give the free version a try and see what you think.
I've been using TabNine for a few weeks, and it's really cool how well it works. My first "woah" moment with it was writing a function where the first thing I wanted to do was take the length of the array, and once I started typing
def foo(bar):
n
it suggested the entire completion of "= len(bar)". It has a really cool way of picking up your coding style that makes it stand out to me.
Aside from the obviously fake jittering gauges, it seems like whenever I reset the page the pointer goes to about 68% and then after 5-10 seconds jumps to 77%. Not sure if it's caching a number and then updating or supposed to make me stay on the page.