Heartquest was FUDGE before FUDGE was cool (shoutout to all the FATE 3.0 folks out there). An introduction to a type of adventure/romance that I had not been exposed to before, it helped bring relationship issues and struggles to the forefront of the story, while using the stereotypes and shorthands developed over time in the source material to get the game off the ground quickly. Steel Roses is one of the supplements for Heartquest, and one of the most detailed and thorough campaign settings for the game.
It focuses on mecha, specifically as plot contrivances in shoujo manga. I know about as much about shoujo manga as a Napoleonic-era carrier pigeon with a severe concussion, so a well-developed sourcebook was a big aid to me. The first and last sections were most valuable to me, as they detailed what mecha were in relation to the characters and gave an example of what a typical setup might be: a 17 year old girl is the only one that can pilot the giant robot that can save the town; her crush, a dreamy 16 year old young man, is secretly part of the resistance against the authorities she is sworn to fight!
The middle portion of the book is a solid, simple, straightforward FUDGE mecha system, with minor tweaks for scale and a few skills and gift/flaws related to mecha. As with most good FUDGE systems, this portion uses the generalized and rules-light nature of FUDGE to make quick and easy generation of player character mechs and enemies fun.
The book references the core Heartquest book quite a lot, so it won't help a standalone FUDGE or mecha game that much. But you should probably buy the core Heartquest book too, so don't complain, just go buy it first.
If you saw Battletech and said "I don't get it, why don't they have green hair and cry about their girlfriends", as so many did, this is the supplement for you.