I never was too much into mecha gaming and I didn't expect to go for this one, but the flexibility of this system and adaptability to any setting I thought of was enough to buy the game.
There are some tweaks which would have to be implemented (eg. targetting based more on size than thermal signature for some settings) but generally the game meets my expectations. You may need to check for errata at MJ12's website as I don't know if the product will be updated with all the corrections.
It allows to play many types of 'mecha' games - from mechanical and steam-powered victorian creations to hard SciFi stuff. For earlier periods you may need to use Size instead of Thermal Signature for targetting though, and you should be fine with it.
I myself am not looking for any other mecha game now :)