I fly with Even More Space on every flight where it's not sold out.
Benefits:
More space
Priority through security (Some airports)
Priority boarding and access to storage
Served first during inflight food/beverage.
Reasonable price
Much higher likelihood that you don't have someone next to you.
Cons:
There are certain legs that seem overpriced for their duration. My usual route (JFK-MSY) has price shifts sometimes that are very confusing. Most of the time it's $45 per leg but I've seen as high as $100.
That being said I pay next to nothing for my upgrades due to Mosaic so that washes out for me.
Did you have any other specific questions?