In my opinion on the maps:
Shatter - Worst map on the game.
Wreckage - Average, but will be a nice add to the BTB playlist.
Harvest - Easily one of the best maps on the game, brilliant map all around. Close, mid and long range parts on it. It has 'hogs and sniper which is always good for big maps . And it feels really balanced too.
I would go for it and buy the maps, just for Harvest lol.