Rusty Android is one of the less played cards in the game. There are several factors to not play with these card and usefulness of this card actually affects the price because it's the cheapest card you can get it on the monster market. It's not that unique card because it can be replaced with more powerful cards with strong, useful abilities. For example Raging Impaler also costs 6 mana but it's way better than Rusty Android. Main disadvantages of this card in my opinion are low speed especially at low levels, only one ability, takes 6 mana which you can use another cost effective cards with more advanced features.
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From @smalien