FeedSpark is a UK based managed service feed company that focuses mostly on Google Shopping. They lack marketplace capabilities and tend to be very expensive, without providing 24/7 full-service support.
Feedonomics on the other hand is one of the best FeedSpark alternatives, with a global 24/7 support team and marketplace and order management capabilities.
What FeedSpark is also missing is customizable alerting capabilities when things go wrong in Google Merchant Center or with custom attributes in your feed.