TLDR AT THE END- I have just checked out the rules in the book and I am here to offer my thoughts. First of all, the character generation system enables for quick character/mech-stats generation and thats pretty cool (also expected by an OSR-based game). One thing key to this game, is the actual melding of the pilot stats and the mecha stats, so your character is the pilot AND the mech. That kinda goes against the spirit of most franchises the game is inspired by (such as Battletech and MS Gundam, where the pilots are somewhat often seen swapping mechs) but it is easily mod-able and does not limit the GM in making and presenting the players with their own unique mecha designs, just by tweaking some stats and upgrades here and there. The upgrades presented for the mechs are very nice, and a solid base to build upon. The weapons, combat and such are solidly represented, powered by the fluidity of the Black Hack's system and a series of very slick modular upgrades that offer many customization options, without making things too complicated. Another thing, the reactor dice is a neat-and-fast mechanic for tracking heat and exertion (Battletech could take a few notes here). The micro-setting presented within the book is a kinda basic sci-fi setting with aliens and various factions, and serves to fuel the reader with ideas and also introduce a person with limited knowledge on mecha to the skeleton of a story they can build upon, all and all, fairly cool stuff. The art and formatting within the book is very nice, with thematic pieces and nice, industrial, cyberpunk-y, black-and-white designs so that's a big plus for me. The extra tokens and paper minis are a nice addition and much appreciated.
TLDR- All and all this is a pretty nice toolkit that a mecha-nerd such as me will find very useful if they want to run a hard, sci-fi giant robot campaign. As a plus, it is quite compatible with other OSR products and adapting other Black Hack supplements will prove very easy. If a GM wants to present different mechs of their own design I would recommend splitting the pilot stats from the mech stats. I am probably going -for my own game- to let the players generate separate stats for their pilots and I am going to create standard arrays for the mechs. I skimmed the book and am already brimming with ideas!